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 $66.58   9.612%   $72.9797   $72.98   $73.00   $73.00  
  Purchase #2 $157.98   11.843%   $176.6896   $176.69   $176.70   $176.70  
  Purchase #3 $119.26   11.492%   $132.9654   $132.97   $132.95   $133.00  
  Purchase #4 $111.45   13.200%   $126.1614   $126.16   $126.15   $126.20  
  Purchase #5 $217.99   12.357%   $244.927   $244.93   $244.95   $244.90  
  Purchase #6 $10.54   13.843%   $11.9991   $12.00   $12.00   $12.00  
  Purchase #7 $118.65   12.676%   $133.6901   $133.69   $133.70   $133.70  
  7 purchase totals = $802.45       $899.4123   $899.42   $899.45   $899.50