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 $212.47   6.467%   $226.2104   $226.21   $226.20   $226.20  
  Purchase #2 $70.52   7.835%   $76.0452   $76.05   $76.05   $76.00  
  Purchase #3 $70.68   7.748%   $76.1563   $76.16   $76.15   $76.20  
  Purchase #4 $179.61   9.636%   $196.9172   $196.92   $196.90   $196.90  
  Purchase #5 $127.71   5.668%   $134.9486   $134.95   $134.95   $134.90  
  Purchase #6 $249.42   7.287%   $267.5952   $267.60   $267.60   $267.60  
  Purchase #7 $7.39   6.266%   $7.8531   $7.85   $7.85   $7.90  
  7 purchase totals = $917.80       $985.7260   $985.74   $985.70   $985.70