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 $62.73   8.662%   $68.1637   $68.16   $68.15   $68.20  
  Purchase #2 $249.39   13.624%   $283.3669   $283.37   $283.35   $283.40  
  Purchase #3 $232.44   9.327%   $254.1197   $254.12   $254.10   $254.10  
  Purchase #4 $239.42   7.543%   $257.4795   $257.48   $257.50   $257.50  
  Purchase #5 $68.95   7.118%   $73.8579   $73.86   $73.85   $73.90  
  Purchase #6 $32.81   8.745%   $35.6792   $35.68   $35.70   $35.70  
  Purchase #7 $160.68   5.610%   $169.6941   $169.69   $169.70   $169.70  
  7 purchase totals = $1,046.42       $1,142.3610   $1,142.36   $1,142.35   $1,142.50