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 $231.75   13.443%   $262.9042   $262.90   $262.90   $262.90  
  Purchase #2 $93.95   7.854%   $101.3288   $101.33   $101.35   $101.30  
  Purchase #3 $217.58   9.462%   $238.1674   $238.17   $238.15   $238.20  
  Purchase #4 $73.64   11.809%   $82.3361   $82.34   $82.35   $82.30  
  Purchase #5 $95.26   13.302%   $107.9315   $107.93   $107.95   $107.90  
  Purchase #6 $217.61   12.793%   $245.4488   $245.45   $245.45   $245.40  
  Purchase #7 $198.93   8.682%   $216.2011   $216.20   $216.20   $216.20  
  7 purchase totals = $1,128.72       $1,254.3179   $1,254.32   $1,254.35   $1,254.20