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 $61.87   12.422%   $69.5555   $69.56   $69.55   $69.60  
  Purchase #2 $59.51   8.335%   $64.4702   $64.47   $64.45   $64.50  
  Purchase #3 $111.39   6.340%   $118.4521   $118.45   $118.45   $118.50  
  Purchase #4 $125.87   3.418%   $130.1722   $130.17   $130.15   $130.20  
  Purchase #5 $241.44   5.217%   $254.0359   $254.04   $254.05   $254.00  
  Purchase #6 $210.38   4.329%   $219.4874   $219.49   $219.50   $219.50  
  Purchase #7 $150.34   10.524%   $166.1618   $166.16   $166.15   $166.20  
  7 purchase totals = $960.80       $1,022.3351   $1,022.34   $1,022.30   $1,022.50