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 $223.96   9.105%   $244.3516   $244.35   $244.35   $244.40  
  Purchase #2 $82.56   6.162%   $87.6473   $87.65   $87.65   $87.60  
  Purchase #3 $189.26   6.482%   $201.5278   $201.53   $201.55   $201.50  
  Purchase #4 $220.99   6.796%   $236.0085   $236.01   $236.00   $236.00  
  Purchase #5 $214.30   8.755%   $233.062   $233.06   $233.05   $233.10  
  Purchase #6 $158.95   4.454%   $166.0296   $166.03   $166.05   $166.00  
  Purchase #7 $51.30   6.462%   $54.615   $54.62   $54.60   $54.60  
  7 purchase totals = $1,141.32       $1,223.2418   $1,223.25   $1,223.25   $1,223.20