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 $96.94   7.297%   $104.0137   $104.01   $104.00   $104.00  
  Purchase #2 $231.43   4.838%   $242.6266   $242.63   $242.65   $242.60  
  Purchase #3 $47.60   9.731%   $52.232   $52.23   $52.25   $52.20  
  Purchase #4 $95.73   5.456%   $100.953   $100.95   $100.95   $101.00  
  Purchase #5 $189.73   5.343%   $199.8673   $199.87   $199.85   $199.90  
  Purchase #6 $229.42   7.247%   $246.0461   $246.05   $246.05   $246.00  
  Purchase #7 $102.77   6.804%   $109.7625   $109.76   $109.75   $109.80  
  7 purchase totals = $993.62       $1,055.5012   $1,055.50   $1,055.50   $1,055.50