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 $104.51   10.322%   $115.2975   $115.30   $115.30   $115.30  
  Purchase #2 $176.39   7.110%   $188.9313   $188.93   $188.95   $188.90  
  Purchase #3 $62.59   11.872%   $70.0207   $70.02   $70.00   $70.00  
  Purchase #4 $179.95   3.131%   $185.5842   $185.58   $185.60   $185.60  
  Purchase #5 $67.58   7.538%   $72.6742   $72.67   $72.65   $72.70  
  Purchase #6 $197.40   10.138%   $217.4124   $217.41   $217.40   $217.40  
  Purchase #7 $18.82   3.797%   $19.5346   $19.53   $19.55   $19.50  
  7 purchase totals = $807.24       $869.4549   $869.44   $869.45   $869.40