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 $58.27   12.564%   $65.591   $65.59   $65.60   $65.60  
  Purchase #2 $59.87   7.648%   $64.4489   $64.45   $64.45   $64.40  
  Purchase #3 $245.84   12.813%   $277.3395   $277.34   $277.35   $277.30  
  Purchase #4 $224.60   12.464%   $252.5941   $252.59   $252.60   $252.60  
  Purchase #5 $9.51   13.843%   $10.8265   $10.83   $10.85   $10.80  
  Purchase #6 $99.51   13.709%   $113.1518   $113.15   $113.15   $113.20  
  Purchase #7 $41.93   5.487%   $44.2307   $44.23   $44.25   $44.20  
  7 purchase totals = $739.53       $828.1825   $828.18   $828.25   $828.10