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 $230.27   5.358%   $242.6079   $242.61   $242.60   $242.60  
  Purchase #2 $56.62   6.557%   $60.3326   $60.33   $60.35   $60.30  
  Purchase #3 $15.69   6.715%   $16.7436   $16.74   $16.75   $16.70  
  Purchase #4 $54.82   9.842%   $60.2154   $60.22   $60.20   $60.20  
  Purchase #5 $202.88   9.872%   $222.9083   $222.91   $222.90   $222.90  
  Purchase #6 $223.63   11.496%   $249.3385   $249.34   $249.35   $249.30  
  Purchase #7 $159.34   3.797%   $165.3901   $165.39   $165.40   $165.40  
  7 purchase totals = $943.25       $1,017.5364   $1,017.54   $1,017.55   $1,017.40