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 $57.58   9.688%   $63.1584   $63.16   $63.15   $63.20  
  Purchase #2 $95.94   11.764%   $107.2264   $107.23   $107.25   $107.20  
  Purchase #3 $199.41   3.446%   $206.2817   $206.28   $206.30   $206.30  
  Purchase #4 $174.79   8.405%   $189.4811   $189.48   $189.50   $189.50  
  Purchase #5 $151.62   11.175%   $168.5635   $168.56   $168.55   $168.60  
  Purchase #6 $241.62   4.861%   $253.3651   $253.37   $253.35   $253.40  
  Purchase #7 $201.31   12.103%   $225.6745   $225.67   $225.65   $225.70  
  7 purchase totals = $1,122.27       $1,213.7507   $1,213.75   $1,213.75   $1,213.90