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 $64.59   8.427%   $70.033   $70.03   $70.05   $70.00  
  Purchase #2 $47.53   4.300%   $49.5738   $49.57   $49.55   $49.60  
  Purchase #3 $215.28   5.221%   $226.5198   $226.52   $226.50   $226.50  
  Purchase #4 $58.49   6.152%   $62.0883   $62.09   $62.10   $62.10  
  Purchase #5 $99.38   13.633%   $112.9285   $112.93   $112.95   $112.90  
  Purchase #6 $149.84   8.127%   $162.0175   $162.02   $162.00   $162.00  
  Purchase #7 $17.73   5.259%   $18.6624   $18.66   $18.65   $18.70  
  7 purchase totals = $652.84       $701.8233   $701.82   $701.80   $701.80