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 $246.25   9.193%   $268.8878   $268.89   $268.90   $268.90  
  Purchase #2 $6.73   13.540%   $7.6412   $7.64   $7.65   $7.60  
  Purchase #3 $233.28   6.339%   $248.0676   $248.07   $248.05   $248.10  
  Purchase #4 $107.83   9.336%   $117.897   $117.90   $117.90   $117.90  
  Purchase #5 $37.52   13.206%   $42.4749   $42.47   $42.45   $42.50  
  Purchase #6 $168.49   4.463%   $176.0097   $176.01   $176.00   $176.00  
  Purchase #7 $76.91   10.867%   $85.2678   $85.27   $85.25   $85.30  
  7 purchase totals = $877.01       $946.2460   $946.25   $946.20   $946.30