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 $227.69   4.532%   $238.0089   $238.01   $238.00   $238.00  
  Purchase #2 $54.97   11.398%   $61.2355   $61.24   $61.25   $61.20  
  Purchase #3 $162.78   3.368%   $168.2624   $168.26   $168.25   $168.30  
  Purchase #4 $140.65   6.107%   $149.2395   $149.24   $149.25   $149.20  
  Purchase #5 $169.45   9.456%   $185.4732   $185.47   $185.45   $185.50  
  Purchase #6 $148.82   5.487%   $156.9858   $156.99   $157.00   $157.00  
  Purchase #7 $88.63   7.197%   $95.0087   $95.01   $95.00   $95.00  
  7 purchase totals = $992.99       $1,054.2140   $1,054.22   $1,054.20   $1,054.20