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 $52.94   8.848%   $57.6241   $57.62   $57.60   $57.60  
  Purchase #2 $136.98   10.237%   $151.0026   $151.00   $151.00   $151.00  
  Purchase #3 $121.68   5.719%   $128.6389   $128.64   $128.65   $128.60  
  Purchase #4 $214.68   6.749%   $229.1688   $229.17   $229.15   $229.20  
  Purchase #5 $112.99   11.704%   $126.2143   $126.21   $126.20   $126.20  
  Purchase #6 $118.37   3.682%   $122.7284   $122.73   $122.75   $122.70  
  Purchase #7 $89.59   10.459%   $98.9602   $98.96   $98.95   $99.00  
  7 purchase totals = $847.23       $914.3373   $914.33   $914.30   $914.30