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 $111.71   11.676%   $124.7533   $124.75   $124.75   $124.80  
  Purchase #2 $118.37   12.552%   $133.2278   $133.23   $133.25   $133.20  
  Purchase #3 $166.35   13.377%   $188.6026   $188.60   $188.60   $188.60  
  Purchase #4 $140.53   9.789%   $154.2865   $154.29   $154.30   $154.30  
  Purchase #5 $24.50   11.636%   $27.3508   $27.35   $27.35   $27.40  
  Purchase #6 $182.58   4.720%   $191.1978   $191.20   $191.20   $191.20  
  Purchase #7 $233.33   7.455%   $250.7248   $250.72   $250.70   $250.70  
  7 purchase totals = $977.37       $1,070.1436   $1,070.14   $1,070.15   $1,070.20