Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $214.25   13.818%   $243.8551   $243.86   $243.85   $243.90  
  Purchase #2 $185.39   4.308%   $193.3766   $193.38   $193.40   $193.40  
  Purchase #3 $123.61   12.464%   $139.0168   $139.02   $139.00   $139.00  
  Purchase #4 $241.47   11.524%   $269.297   $269.30   $269.30   $269.30  
  Purchase #5 $107.37   12.489%   $120.7794   $120.78   $120.80   $120.80  
  Purchase #6 $145.89   13.306%   $165.3021   $165.30   $165.30   $165.30  
  Purchase #7 $173.43   8.599%   $188.3432   $188.34   $188.35   $188.30  
  7 purchase totals = $1,191.41       $1,319.9702   $1,319.98   $1,320.00   $1,320.00