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 $147.40   5.766%   $155.8991   $155.90   $155.90   $155.90  
  Purchase #2 $123.29   5.290%   $129.812   $129.81   $129.80   $129.80  
  Purchase #3 $164.74   3.234%   $170.0677   $170.07   $170.05   $170.10  
  Purchase #4 $114.70   12.308%   $128.8173   $128.82   $128.80   $128.80  
  Purchase #5 $41.67   13.114%   $47.1346   $47.13   $47.15   $47.10  
  Purchase #6 $79.43   4.676%   $83.1441   $83.14   $83.15   $83.10  
  Purchase #7 $166.43   4.486%   $173.896   $173.90   $173.90   $173.90  
  7 purchase totals = $837.66       $888.7708   $888.77   $888.75   $888.70