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 $62.68   6.868%   $66.9849   $66.98   $67.00   $67.00  
  Purchase #2 $190.77   5.324%   $200.9266   $200.93   $200.95   $200.90  
  Purchase #3 $88.50   6.124%   $93.9197   $93.92   $93.90   $93.90  
  Purchase #4 $117.78   6.568%   $125.5158   $125.52   $125.50   $125.50  
  Purchase #5 $192.79   4.667%   $201.7875   $201.79   $201.80   $201.80  
  Purchase #6 $249.56   8.592%   $271.0022   $271.00   $271.00   $271.00  
  Purchase #7 $194.68   11.632%   $217.3252   $217.33   $217.35   $217.30  
  7 purchase totals = $1,096.76       $1,177.4619   $1,177.47   $1,177.50   $1,177.40