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 $164.87   8.339%   $178.6185   $178.62   $178.60   $178.60  
  Purchase #2 $102.47   11.502%   $114.2561   $114.26   $114.25   $114.30  
  Purchase #3 $226.54   10.658%   $250.6846   $250.68   $250.70   $250.70  
  Purchase #4 $125.92   13.838%   $143.3448   $143.34   $143.35   $143.30  
  Purchase #5 $125.25   7.113%   $134.159   $134.16   $134.15   $134.20  
  Purchase #6 $107.92   9.803%   $118.4994   $118.50   $118.50   $118.50  
  Purchase #7 $91.96   4.763%   $96.3401   $96.34   $96.35   $96.30  
  7 purchase totals = $944.93       $1,035.9025   $1,035.90   $1,035.90   $1,035.90