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 $228.29   9.162%   $249.2059   $249.21   $249.20   $249.20  
  Purchase #2 $57.64   10.591%   $63.7447   $63.74   $63.75   $63.70  
  Purchase #3 $150.32   12.279%   $168.7778   $168.78   $168.80   $168.80  
  Purchase #4 $196.46   8.870%   $213.886   $213.89   $213.90   $213.90  
  Purchase #5 $221.57   10.127%   $244.0084   $244.01   $244.00   $244.00  
  Purchase #6 $73.75   11.228%   $82.0307   $82.03   $82.05   $82.00  
  Purchase #7 $140.50   12.170%   $157.5989   $157.60   $157.60   $157.60  
  7 purchase totals = $1,068.53       $1,179.2524   $1,179.26   $1,179.30   $1,179.20