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 $27.40   4.272%   $28.5705   $28.57   $28.55   $28.60  
  Purchase #2 $96.40   3.810%   $100.0728   $100.07   $100.05   $100.10  
  Purchase #3 $90.50   13.278%   $102.5166   $102.52   $102.50   $102.50  
  Purchase #4 $49.88   9.727%   $54.7318   $54.73   $54.75   $54.70  
  Purchase #5 $72.39   4.739%   $75.8206   $75.82   $75.80   $75.80  
  Purchase #6 $108.49   7.139%   $116.2351   $116.24   $116.25   $116.20  
  Purchase #7 $193.71   4.401%   $202.2352   $202.24   $202.25   $202.20  
  7 purchase totals = $638.77       $680.1826   $680.19   $680.15   $680.10