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 $184.82   11.708%   $206.4587   $206.46   $206.45   $206.50  
  Purchase #2 $112.68   9.414%   $123.2877   $123.29   $123.30   $123.30  
  Purchase #3 $57.84   7.526%   $62.193   $62.19   $62.20   $62.20  
  Purchase #4 $242.96   10.567%   $268.6336   $268.63   $268.65   $268.60  
  Purchase #5 $210.57   11.180%   $234.1117   $234.11   $234.10   $234.10  
  Purchase #6 $139.42   5.824%   $147.5398   $147.54   $147.55   $147.50  
  Purchase #7 $146.86   11.705%   $164.05   $164.05   $164.05   $164.10  
  7 purchase totals = $1,095.15       $1,206.2745   $1,206.27   $1,206.30   $1,206.30