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 $119.90   6.425%   $127.6036   $127.60   $127.60   $127.60  
  Purchase #2 $223.73   5.197%   $235.3572   $235.36   $235.35   $235.40  
  Purchase #3 $14.53   10.177%   $16.0087   $16.01   $16.00   $16.00  
  Purchase #4 $91.83   11.403%   $102.3014   $102.30   $102.30   $102.30  
  Purchase #5 $157.37   7.102%   $168.5464   $168.55   $168.55   $168.50  
  Purchase #6 $135.62   13.546%   $153.9911   $153.99   $154.00   $154.00  
  Purchase #7 $119.61   6.424%   $127.2937   $127.29   $127.30   $127.30  
  7 purchase totals = $862.59       $931.1021   $931.10   $931.10   $931.10