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 $208.44   13.116%   $235.779   $235.78   $235.80   $235.80  
  Purchase #2 $28.90   3.166%   $29.815   $29.82   $29.80   $29.80  
  Purchase #3 $244.99   9.399%   $268.0166   $268.02   $268.00   $268.00  
  Purchase #4 $6.45   11.674%   $7.203   $7.20   $7.20   $7.20  
  Purchase #5 $51.83   10.480%   $57.2618   $57.26   $57.25   $57.30  
  Purchase #6 $196.86   11.337%   $219.178   $219.18   $219.20   $219.20  
  Purchase #7 $8.26   10.799%   $9.152   $9.15   $9.15   $9.20  
  7 purchase totals = $745.73       $826.4054   $826.41   $826.40   $826.50