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 $138.53   12.859%   $156.3436   $156.34   $156.35   $156.30  
  Purchase #2 $206.57   8.717%   $224.5767   $224.58   $224.60   $224.60  
  Purchase #3 $10.56   8.388%   $11.4458   $11.45   $11.45   $11.40  
  Purchase #4 $248.25   11.256%   $276.193   $276.19   $276.20   $276.20  
  Purchase #5 $223.45   13.500%   $253.6158   $253.62   $253.60   $253.60  
  Purchase #6 $48.85   10.420%   $53.9402   $53.94   $53.95   $53.90  
  Purchase #7 $60.46   10.779%   $66.977   $66.98   $67.00   $67.00  
  7 purchase totals = $936.67       $1,043.0921   $1,043.10   $1,043.15   $1,043.00