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 $62.42   13.533%   $70.8673   $70.87   $70.85   $70.90  
  Purchase #2 $139.62   9.349%   $152.6731   $152.67   $152.65   $152.70  
  Purchase #3 $63.95   6.830%   $68.3178   $68.32   $68.30   $68.30  
  Purchase #4 $41.82   6.387%   $44.491   $44.49   $44.50   $44.50  
  Purchase #5 $97.31   13.755%   $110.695   $110.70   $110.70   $110.70  
  Purchase #6 $203.75   8.433%   $220.9322   $220.93   $220.95   $220.90  
  Purchase #7 $162.47   9.509%   $177.9193   $177.92   $177.90   $177.90  
  7 purchase totals = $771.34       $845.8957   $845.90   $845.85   $845.90