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 $225.26   10.362%   $248.6014   $248.60   $248.60   $248.60  
  Purchase #2 $31.25   8.597%   $33.9366   $33.94   $33.95   $33.90  
  Purchase #3 $180.39   11.502%   $201.1385   $201.14   $201.15   $201.10  
  Purchase #4 $66.28   7.570%   $71.2974   $71.30   $71.30   $71.30  
  Purchase #5 $125.94   11.558%   $140.4961   $140.50   $140.50   $140.50  
  Purchase #6 $180.40   7.717%   $194.3215   $194.32   $194.30   $194.30  
  Purchase #7 $247.63   11.246%   $275.4785   $275.48   $275.50   $275.50  
  7 purchase totals = $1,057.15       $1,165.2700   $1,165.28   $1,165.30   $1,165.20