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 $204.36   13.689%   $232.3348   $232.33   $232.35   $232.30  
  Purchase #2 $24.47   5.229%   $25.7495   $25.75   $25.75   $25.70  
  Purchase #3 $67.53   7.697%   $72.7278   $72.73   $72.75   $72.70  
  Purchase #4 $170.50   12.376%   $191.6011   $191.60   $191.60   $191.60  
  Purchase #5 $80.42   11.573%   $89.727   $89.73   $89.75   $89.70  
  Purchase #6 $189.41   7.653%   $203.9055   $203.91   $203.90   $203.90  
  Purchase #7 $214.40   9.112%   $233.9361   $233.94   $233.95   $233.90  
  7 purchase totals = $951.09       $1,049.9818   $1,049.99   $1,050.05   $1,049.80