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 $38.90   11.699%   $43.4509   $43.45   $43.45   $43.50  
  Purchase #2 $224.43   9.813%   $246.4533   $246.45   $246.45   $246.50  
  Purchase #3 $171.96   6.757%   $183.5793   $183.58   $183.60   $183.60  
  Purchase #4 $88.54   5.394%   $93.3158   $93.32   $93.30   $93.30  
  Purchase #5 $68.58   13.741%   $78.0036   $78.00   $78.00   $78.00  
  Purchase #6 $241.72   5.184%   $254.2508   $254.25   $254.25   $254.30  
  Purchase #7 $110.28   6.277%   $117.2023   $117.20   $117.20   $117.20  
  7 purchase totals = $944.41       $1,016.2560   $1,016.25   $1,016.25   $1,016.40