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 $189.47   6.765%   $202.2876   $202.29   $202.30   $202.30  
  Purchase #2 $56.92   9.488%   $62.3206   $62.32   $62.30   $62.30  
  Purchase #3 $244.88   8.513%   $265.7266   $265.73   $265.75   $265.70  
  Purchase #4 $11.39   10.770%   $12.6167   $12.62   $12.60   $12.60  
  Purchase #5 $132.57   6.694%   $141.4442   $141.44   $141.45   $141.40  
  Purchase #6 $232.30   13.549%   $263.7743   $263.77   $263.75   $263.80  
  Purchase #7 $16.41   3.531%   $16.9894   $16.99   $17.00   $17.00  
  7 purchase totals = $883.94       $965.1594   $965.16   $965.15   $965.10