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 $93.53   13.574%   $106.2258   $106.23   $106.25   $106.20  
  Purchase #2 $113.86   11.819%   $127.3171   $127.32   $127.30   $127.30  
  Purchase #3 $151.36   12.583%   $170.4056   $170.41   $170.40   $170.40  
  Purchase #4 $187.87   5.760%   $198.6913   $198.69   $198.70   $198.70  
  Purchase #5 $66.35   13.622%   $75.3882   $75.39   $75.40   $75.40  
  Purchase #6 $38.53   6.136%   $40.8942   $40.89   $40.90   $40.90  
  Purchase #7 $116.79   5.331%   $123.0161   $123.02   $123.00   $123.00  
  7 purchase totals = $768.29       $841.9383   $841.95   $841.95   $841.90