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 $141.81   11.249%   $157.7622   $157.76   $157.75   $157.80  
  Purchase #2 $199.57   13.223%   $225.9591   $225.96   $225.95   $226.00  
  Purchase #3 $88.68   4.525%   $92.6928   $92.69   $92.70   $92.70  
  Purchase #4 $152.92   9.614%   $167.6217   $167.62   $167.60   $167.60  
  Purchase #5 $22.34   8.579%   $24.2565   $24.26   $24.25   $24.30  
  Purchase #6 $111.91   11.697%   $125.0001   $125.00   $125.00   $125.00  
  Purchase #7 $115.72   11.764%   $129.3333   $129.33   $129.35   $129.30  
  7 purchase totals = $832.95       $922.6257   $922.62   $922.60   $922.70