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 $119.95   10.794%   $132.8974   $132.90   $132.90   $132.90  
  Purchase #2 $160.65   10.178%   $177.001   $177.00   $177.00   $177.00  
  Purchase #3 $65.30   3.306%   $67.4588   $67.46   $67.45   $67.50  
  Purchase #4 $48.60   13.767%   $55.2908   $55.29   $55.30   $55.30  
  Purchase #5 $184.78   4.124%   $192.4003   $192.40   $192.40   $192.40  
  Purchase #6 $155.50   7.182%   $166.668   $166.67   $166.65   $166.70  
  Purchase #7 $86.75   4.197%   $90.3909   $90.39   $90.40   $90.40  
  7 purchase totals = $821.53       $882.1072   $882.11   $882.10   $882.20