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 $63.34   7.348%   $67.9942   $67.99   $68.00   $68.00  
  Purchase #2 $213.31   10.810%   $236.3688   $236.37   $236.35   $236.40  
  Purchase #3 $139.98   8.102%   $151.3212   $151.32   $151.30   $151.30  
  Purchase #4 $33.95   10.607%   $37.5511   $37.55   $37.55   $37.60  
  Purchase #5 $100.29   7.203%   $107.5139   $107.51   $107.50   $107.50  
  Purchase #6 $202.47   7.849%   $218.3619   $218.36   $218.35   $218.40  
  Purchase #7 $205.77   4.389%   $214.8012   $214.80   $214.80   $214.80  
  7 purchase totals = $959.11       $1,033.9123   $1,033.90   $1,033.85   $1,034.00