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 $214.27   12.839%   $241.7801   $241.78   $241.80   $241.80  
  Purchase #2 $242.26   11.218%   $269.4367   $269.44   $269.45   $269.40  
  Purchase #3 $127.71   4.110%   $132.9589   $132.96   $132.95   $133.00  
  Purchase #4 $206.85   8.677%   $224.7984   $224.80   $224.80   $224.80  
  Purchase #5 $206.75   13.498%   $234.6571   $234.66   $234.65   $234.70  
  Purchase #6 $27.37   5.378%   $28.842   $28.84   $28.85   $28.80  
  Purchase #7 $160.65   13.430%   $182.2253   $182.23   $182.25   $182.20  
  7 purchase totals = $1,185.86       $1,314.6985   $1,314.71   $1,314.75   $1,314.70