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 $62.96   11.707%   $70.3307   $70.33   $70.35   $70.30  
  Purchase #2 $98.72   5.385%   $104.0361   $104.04   $104.05   $104.00  
  Purchase #3 $133.52   9.693%   $146.4621   $146.46   $146.45   $146.50  
  Purchase #4 $163.36   3.442%   $168.9829   $168.98   $169.00   $169.00  
  Purchase #5 $17.76   6.699%   $18.9497   $18.95   $18.95   $18.90  
  Purchase #6 $57.31   13.276%   $64.9185   $64.92   $64.90   $64.90  
  Purchase #7 $187.59   3.422%   $194.0093   $194.01   $194.00   $194.00  
  7 purchase totals = $721.22       $767.6893   $767.69   $767.70   $767.60