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 $59.64   11.136%   $66.2815   $66.28   $66.30   $66.30  
  Purchase #2 $130.87   12.829%   $147.6593   $147.66   $147.65   $147.70  
  Purchase #3 $52.27   9.669%   $57.324   $57.32   $57.30   $57.30  
  Purchase #4 $101.79   8.845%   $110.7933   $110.79   $110.80   $110.80  
  Purchase #5 $165.80   13.216%   $187.7121   $187.71   $187.70   $187.70  
  Purchase #6 $148.85   5.599%   $157.1841   $157.18   $157.20   $157.20  
  Purchase #7 $54.83   11.851%   $61.3279   $61.33   $61.35   $61.30  
  7 purchase totals = $714.05       $788.2822   $788.27   $788.30   $788.30