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 $36.82   3.289%   $38.031   $38.03   $38.05   $38.00  
  Purchase #2 $84.49   4.177%   $88.0191   $88.02   $88.00   $88.00  
  Purchase #3 $88.29   8.524%   $95.8158   $95.82   $95.80   $95.80  
  Purchase #4 $185.82   4.756%   $194.6576   $194.66   $194.65   $194.70  
  Purchase #5 $183.64   10.681%   $203.2546   $203.25   $203.25   $203.30  
  Purchase #6 $150.51   11.157%   $167.3024   $167.30   $167.30   $167.30  
  Purchase #7 $176.89   9.618%   $193.9033   $193.90   $193.90   $193.90  
  7 purchase totals = $906.46       $980.9838   $980.98   $980.95   $981.00