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 $134.76   10.381%   $148.7494   $148.75   $148.75   $148.70  
  Purchase #2 $65.35   5.456%   $68.9155   $68.92   $68.90   $68.90  
  Purchase #3 $175.51   10.580%   $194.079   $194.08   $194.10   $194.10  
  Purchase #4 $14.40   8.278%   $15.592   $15.59   $15.60   $15.60  
  Purchase #5 $85.90   13.541%   $97.5317   $97.53   $97.55   $97.50  
  Purchase #6 $212.33   6.139%   $225.3649   $225.36   $225.35   $225.40  
  Purchase #7 $8.99   9.432%   $9.8379   $9.84   $9.85   $9.80  
  7 purchase totals = $697.24       $760.0704   $760.07   $760.10   $760.00