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 $58.47   8.733%   $63.5762   $63.58   $63.60   $63.60  
  Purchase #2 $219.27   10.613%   $242.5411   $242.54   $242.55   $242.50  
  Purchase #3 $134.96   8.645%   $146.6273   $146.63   $146.65   $146.60  
  Purchase #4 $224.56   8.160%   $242.8841   $242.88   $242.90   $242.90  
  Purchase #5 $41.43   3.858%   $43.0284   $43.03   $43.05   $43.00  
  Purchase #6 $112.36   12.508%   $126.414   $126.41   $126.40   $126.40  
  Purchase #7 $213.67   5.763%   $225.9838   $225.98   $226.00   $226.00  
  7 purchase totals = $1,004.72       $1,091.0549   $1,091.05   $1,091.15   $1,091.00