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 $173.89   5.391%   $183.2644   $183.26   $183.25   $183.30  
  Purchase #2 $232.93   7.426%   $250.2274   $250.23   $250.25   $250.20  
  Purchase #3 $91.71   4.347%   $95.6966   $95.70   $95.70   $95.70  
  Purchase #4 $196.57   7.161%   $210.6464   $210.65   $210.65   $210.60  
  Purchase #5 $228.71   6.121%   $242.7093   $242.71   $242.70   $242.70  
  Purchase #6 $221.60   10.312%   $244.4514   $244.45   $244.45   $244.50  
  Purchase #7 $48.44   4.534%   $50.6363   $50.64   $50.65   $50.60  
  7 purchase totals = $1,193.85       $1,277.6318   $1,277.64   $1,277.65   $1,277.60