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 $187.93   10.659%   $207.9615   $207.96   $207.95   $208.00  
  Purchase #2 $61.55   9.844%   $67.609   $67.61   $67.60   $67.60  
  Purchase #3 $147.38   10.799%   $163.2956   $163.30   $163.30   $163.30  
  Purchase #4 $184.45   7.655%   $198.5696   $198.57   $198.55   $198.60  
  Purchase #5 $32.33   12.626%   $36.412   $36.41   $36.40   $36.40  
  Purchase #6 $14.68   10.709%   $16.2521   $16.25   $16.25   $16.30  
  Purchase #7 $57.56   11.643%   $64.2617   $64.26   $64.25   $64.30  
  7 purchase totals = $685.88       $754.3615   $754.36   $754.30   $754.50