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 $233.47   8.774%   $253.9547   $253.95   $253.95   $254.00  
  Purchase #2 $91.74   5.868%   $97.1233   $97.12   $97.10   $97.10  
  Purchase #3 $223.89   7.229%   $240.075   $240.08   $240.10   $240.10  
  Purchase #4 $31.35   3.479%   $32.4407   $32.44   $32.45   $32.40  
  Purchase #5 $214.78   8.287%   $232.5788   $232.58   $232.60   $232.60  
  Purchase #6 $68.38   10.752%   $75.7322   $75.73   $75.75   $75.70  
  Purchase #7 $24.33   5.528%   $25.675   $25.68   $25.70   $25.70  
  7 purchase totals = $887.94       $957.5797   $957.58   $957.65   $957.60