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 $151.33   10.266%   $166.8655   $166.87   $166.85   $166.90  
  Purchase #2 $128.49   8.426%   $139.3166   $139.32   $139.30   $139.30  
  Purchase #3 $164.59   7.846%   $177.5037   $177.50   $177.50   $177.50  
  Purchase #4 $250.93   13.562%   $284.9611   $284.96   $284.95   $285.00  
  Purchase #5 $158.40   4.570%   $165.6389   $165.64   $165.65   $165.60  
  Purchase #6 $238.72   12.699%   $269.0351   $269.04   $269.05   $269.00  
  Purchase #7 $187.82   13.719%   $213.587   $213.59   $213.60   $213.60  
  7 purchase totals = $1,280.28       $1,416.9079   $1,416.92   $1,416.90   $1,416.90