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 $246.62   5.804%   $260.9338   $260.93   $260.95   $260.90  
  Purchase #2 $9.48   9.359%   $10.3672   $10.37   $10.35   $10.40  
  Purchase #3 $43.69   6.414%   $46.4923   $46.49   $46.50   $46.50  
  Purchase #4 $158.30   4.336%   $165.1639   $165.16   $165.15   $165.20  
  Purchase #5 $96.28   3.141%   $99.3042   $99.30   $99.30   $99.30  
  Purchase #6 $156.59   12.374%   $175.9664   $175.97   $175.95   $176.00  
  Purchase #7 $232.88   8.263%   $252.1229   $252.12   $252.10   $252.10  
  7 purchase totals = $943.84       $1,010.3507   $1,010.34   $1,010.30   $1,010.40