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 $65.30   6.269%   $69.3937   $69.39   $69.40   $69.40  
  Purchase #2 $187.65   9.105%   $204.7355   $204.74   $204.75   $204.70  
  Purchase #3 $108.43   7.516%   $116.5796   $116.58   $116.60   $116.60  
  Purchase #4 $32.54   3.317%   $33.6194   $33.62   $33.60   $33.60  
  Purchase #5 $55.92   5.330%   $58.9005   $58.90   $58.90   $58.90  
  Purchase #6 $230.69   12.790%   $260.1953   $260.20   $260.20   $260.20  
  Purchase #7 $238.74   4.112%   $248.557   $248.56   $248.55   $248.60  
  7 purchase totals = $919.27       $991.9810   $991.99   $992.00   $992.00