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 $43.36   12.427%   $48.7483   $48.75   $48.75   $48.70  
  Purchase #2 $230.42   10.680%   $255.0289   $255.03   $255.05   $255.00  
  Purchase #3 $23.33   3.117%   $24.0572   $24.06   $24.05   $24.10  
  Purchase #4 $217.30   6.585%   $231.6092   $231.61   $231.60   $231.60  
  Purchase #5 $72.44   13.607%   $82.2969   $82.30   $82.30   $82.30  
  Purchase #6 $213.40   8.775%   $232.1259   $232.13   $232.15   $232.10  
  Purchase #7 $149.76   8.361%   $162.2814   $162.28   $162.30   $162.30  
  7 purchase totals = $950.01       $1,036.1478   $1,036.16   $1,036.20   $1,036.10