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 $204.61   11.667%   $228.4818   $228.48   $228.50   $228.50  
  Purchase #2 $21.54   7.373%   $23.1281   $23.13   $23.15   $23.10  
  Purchase #3 $72.88   5.278%   $76.7266   $76.73   $76.75   $76.70  
  Purchase #4 $89.33   10.422%   $98.64   $98.64   $98.65   $98.60  
  Purchase #5 $143.86   9.832%   $158.0043   $158.00   $158.00   $158.00  
  Purchase #6 $226.28   12.523%   $254.617   $254.62   $254.60   $254.60  
  Purchase #7 $220.48   3.478%   $228.1483   $228.15   $228.15   $228.10  
  7 purchase totals = $978.98       $1,067.7461   $1,067.75   $1,067.80   $1,067.60