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 $238.50   6.473%   $253.9381   $253.94   $253.95   $253.90  
  Purchase #2 $6.62   6.614%   $7.0578   $7.06   $7.05   $7.10  
  Purchase #3 $126.91   5.611%   $134.0309   $134.03   $134.05   $134.00  
  Purchase #4 $136.53   11.553%   $152.3033   $152.30   $152.30   $152.30  
  Purchase #5 $146.73   4.276%   $153.0042   $153.00   $153.00   $153.00  
  Purchase #6 $69.40   5.821%   $73.4398   $73.44   $73.45   $73.40  
  Purchase #7 $149.69   13.216%   $169.473   $169.47   $169.45   $169.50  
  7 purchase totals = $874.38       $943.2471   $943.24   $943.25   $943.20