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 $208.82   10.758%   $231.2849   $231.28   $231.30   $231.30  
  Purchase #2 $184.84   4.607%   $193.3556   $193.36   $193.35   $193.40  
  Purchase #3 $195.79   3.191%   $202.0377   $202.04   $202.05   $202.00  
  Purchase #4 $16.63   5.431%   $17.5332   $17.53   $17.55   $17.50  
  Purchase #5 $138.43   11.255%   $154.0103   $154.01   $154.00   $154.00  
  Purchase #6 $75.86   6.627%   $80.8872   $80.89   $80.90   $80.90  
  Purchase #7 $13.54   13.451%   $15.3613   $15.36   $15.35   $15.40  
  7 purchase totals = $833.91       $894.4702   $894.47   $894.50   $894.50