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 $159.92   10.658%   $176.9643   $176.96   $176.95   $177.00  
  Purchase #2 $32.79   5.541%   $34.6069   $34.61   $34.60   $34.60  
  Purchase #3 $154.77   12.585%   $174.2478   $174.25   $174.25   $174.20  
  Purchase #4 $38.43   7.221%   $41.205   $41.21   $41.20   $41.20  
  Purchase #5 $41.94   9.105%   $45.7586   $45.76   $45.75   $45.80  
  Purchase #6 $219.42   11.470%   $244.5875   $244.59   $244.60   $244.60  
  Purchase #7 $56.39   12.259%   $63.3029   $63.30   $63.30   $63.30  
  7 purchase totals = $703.66       $780.6730   $780.68   $780.65   $780.70