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 $59.97   8.393%   $65.0033   $65.00   $65.00   $65.00  
  Purchase #2 $42.94   5.634%   $45.3592   $45.36   $45.35   $45.40  
  Purchase #3 $85.34   7.292%   $91.563   $91.56   $91.55   $91.60  
  Purchase #4 $77.96   12.742%   $87.8937   $87.89   $87.90   $87.90  
  Purchase #5 $169.93   5.600%   $179.4461   $179.45   $179.45   $179.40  
  Purchase #6 $179.32   13.762%   $203.998   $204.00   $204.00   $204.00  
  Purchase #7 $134.88   3.590%   $139.7222   $139.72   $139.70   $139.70  
  7 purchase totals = $750.34       $812.9855   $812.98   $812.95   $813.00