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 $247.30   6.341%   $262.9813   $262.98   $263.00   $263.00  
  Purchase #2 $98.95   7.195%   $106.0695   $106.07   $106.05   $106.10  
  Purchase #3 $237.60   4.660%   $248.6722   $248.67   $248.65   $248.70  
  Purchase #4 $78.88   3.313%   $81.4933   $81.49   $81.50   $81.50  
  Purchase #5 $44.52   12.733%   $50.1887   $50.19   $50.20   $50.20  
  Purchase #6 $228.36   10.347%   $251.9884   $251.99   $252.00   $252.00  
  Purchase #7 $77.73   5.459%   $81.9733   $81.97   $81.95   $82.00  
  7 purchase totals = $1,013.34       $1,083.3667   $1,083.36   $1,083.35   $1,083.50