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 $241.87   8.733%   $262.9925   $262.99   $263.00   $263.00  
  Purchase #2 $96.86   13.443%   $109.8809   $109.88   $109.90   $109.90  
  Purchase #3 $38.76   6.186%   $41.1577   $41.16   $41.15   $41.20  
  Purchase #4 $110.87   13.264%   $125.5758   $125.58   $125.60   $125.60  
  Purchase #5 $150.40   5.810%   $159.1382   $159.14   $159.15   $159.10  
  Purchase #6 $62.40   3.455%   $64.5559   $64.56   $64.55   $64.60  
  Purchase #7 $227.87   11.394%   $253.8335   $253.83   $253.85   $253.80  
  7 purchase totals = $929.03       $1,017.1345   $1,017.14   $1,017.20   $1,017.20