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 $140.40   6.106%   $148.9728   $148.97   $148.95   $149.00  
  Purchase #2 $205.74   9.358%   $224.9931   $224.99   $225.00   $225.00  
  Purchase #3 $17.42   4.828%   $18.261   $18.26   $18.25   $18.30  
  Purchase #4 $226.48   13.153%   $256.2689   $256.27   $256.25   $256.30  
  Purchase #5 $198.61   11.810%   $222.0658   $222.07   $222.05   $222.10  
  Purchase #6 $200.60   12.145%   $224.9629   $224.96   $224.95   $225.00  
  Purchase #7 $98.56   13.753%   $112.115   $112.12   $112.10   $112.10  
  7 purchase totals = $1,087.81       $1,207.6395   $1,207.64   $1,207.55   $1,207.80