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 $59.92   6.649%   $63.9041   $63.90   $63.90   $63.90  
  Purchase #2 $217.87   11.573%   $243.0841   $243.08   $243.10   $243.10  
  Purchase #3 $71.40   8.501%   $77.4697   $77.47   $77.45   $77.50  
  Purchase #4 $144.73   5.390%   $152.5309   $152.53   $152.55   $152.50  
  Purchase #5 $235.96   3.512%   $244.2469   $244.25   $244.25   $244.20  
  Purchase #6 $12.41   4.419%   $12.9584   $12.96   $12.95   $13.00  
  Purchase #7 $93.30   4.433%   $97.436   $97.44   $97.45   $97.40  
  7 purchase totals = $835.59       $891.6301   $891.63   $891.65   $891.60