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 $42.41   10.432%   $46.8342   $46.83   $46.85   $46.80  
  Purchase #2 $188.85   8.727%   $205.3309   $205.33   $205.35   $205.30  
  Purchase #3 $25.73   5.556%   $27.1596   $27.16   $27.15   $27.20  
  Purchase #4 $148.85   4.841%   $156.0558   $156.06   $156.05   $156.10  
  Purchase #5 $190.28   11.626%   $212.402   $212.40   $212.40   $212.40  
  Purchase #6 $60.34   9.300%   $65.9516   $65.95   $65.95   $66.00  
  Purchase #7 $194.53   11.765%   $217.4165   $217.42   $217.40   $217.40  
  7 purchase totals = $850.99       $931.1506   $931.15   $931.15   $931.20