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 $85.83   13.417%   $97.3458   $97.35   $97.35   $97.30  
  Purchase #2 $88.45   8.113%   $95.6259   $95.63   $95.65   $95.60  
  Purchase #3 $171.82   6.432%   $182.8715   $182.87   $182.85   $182.90  
  Purchase #4 $65.54   8.190%   $70.9077   $70.91   $70.90   $70.90  
  Purchase #5 $162.70   9.642%   $178.3875   $178.39   $178.40   $178.40  
  Purchase #6 $61.76   4.829%   $64.7424   $64.74   $64.75   $64.70  
  Purchase #7 $35.86   12.410%   $40.3102   $40.31   $40.30   $40.30  
  7 purchase totals = $671.96       $730.1910   $730.20   $730.20   $730.10