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 $213.62   12.599%   $240.534   $240.53   $240.55   $240.50  
  Purchase #2 $41.25   8.610%   $44.8016   $44.80   $44.80   $44.80  
  Purchase #3 $65.69   9.564%   $71.9726   $71.97   $71.95   $72.00  
  Purchase #4 $90.43   13.620%   $102.7466   $102.75   $102.75   $102.70  
  Purchase #5 $214.81   5.471%   $226.5623   $226.56   $226.55   $226.60  
  Purchase #6 $200.25   6.569%   $213.4044   $213.40   $213.40   $213.40  
  Purchase #7 $118.94   9.550%   $130.2988   $130.30   $130.30   $130.30  
  7 purchase totals = $944.99       $1,030.3203   $1,030.31   $1,030.30   $1,030.30