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 $243.69   4.606%   $254.9144   $254.91   $254.90   $254.90  
  Purchase #2 $216.62   3.485%   $224.1692   $224.17   $224.15   $224.20  
  Purchase #3 $84.95   11.791%   $94.9665   $94.97   $94.95   $95.00  
  Purchase #4 $12.84   10.869%   $14.2356   $14.24   $14.25   $14.20  
  Purchase #5 $93.61   10.613%   $103.5448   $103.54   $103.55   $103.50  
  Purchase #6 $60.31   5.377%   $63.5529   $63.55   $63.55   $63.60  
  Purchase #7 $46.80   3.666%   $48.5157   $48.52   $48.50   $48.50  
  7 purchase totals = $758.82       $803.8991   $803.90   $803.85   $803.90