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 $56.27   4.257%   $58.6654   $58.67   $58.65   $58.70  
  Purchase #2 $91.48   12.511%   $102.9251   $102.93   $102.95   $102.90  
  Purchase #3 $80.71   8.367%   $87.463   $87.46   $87.45   $87.50  
  Purchase #4 $214.72   13.727%   $244.1946   $244.19   $244.20   $244.20  
  Purchase #5 $63.32   10.434%   $69.9268   $69.93   $69.95   $69.90  
  Purchase #6 $33.61   8.121%   $36.3395   $36.34   $36.35   $36.30  
  Purchase #7 $177.54   6.444%   $188.9807   $188.98   $189.00   $189.00  
  7 purchase totals = $717.65       $788.4951   $788.50   $788.55   $788.50