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 $206.68   7.418%   $222.0115   $222.01   $222.00   $222.00  
  Purchase #2 $215.82   13.739%   $245.4715   $245.47   $245.45   $245.50  
  Purchase #3 $67.51   8.513%   $73.2571   $73.26   $73.25   $73.30  
  Purchase #4 $177.89   3.590%   $184.2763   $184.28   $184.30   $184.30  
  Purchase #5 $30.96   11.842%   $34.6263   $34.63   $34.65   $34.60  
  Purchase #6 $155.65   6.721%   $166.1112   $166.11   $166.10   $166.10  
  Purchase #7 $14.63   12.402%   $16.4444   $16.44   $16.45   $16.40  
  7 purchase totals = $869.14       $942.1983   $942.20   $942.20   $942.20