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 $61.71   6.716%   $65.8544   $65.85   $65.85   $65.90  
  Purchase #2 $206.77   9.149%   $225.6874   $225.69   $225.70   $225.70  
  Purchase #3 $187.37   3.649%   $194.2071   $194.21   $194.20   $194.20  
  Purchase #4 $124.60   11.335%   $138.7234   $138.72   $138.70   $138.70  
  Purchase #5 $51.96   13.483%   $58.9658   $58.97   $58.95   $59.00  
  Purchase #6 $101.36   3.379%   $104.785   $104.79   $104.80   $104.80  
  Purchase #7 $215.70   7.800%   $232.5246   $232.52   $232.50   $232.50  
  7 purchase totals = $949.47       $1,020.7477   $1,020.75   $1,020.70   $1,020.80