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 $71.60   6.180%   $76.0249   $76.02   $76.00   $76.00  
  Purchase #2 $116.60   12.232%   $130.8625   $130.86   $130.85   $130.90  
  Purchase #3 $230.71   10.141%   $254.1063   $254.11   $254.10   $254.10  
  Purchase #4 $207.59   10.363%   $229.1026   $229.10   $229.10   $229.10  
  Purchase #5 $231.47   10.200%   $255.0799   $255.08   $255.10   $255.10  
  Purchase #6 $233.63   3.150%   $240.9893   $240.99   $241.00   $241.00  
  Purchase #7 $107.93   6.392%   $114.8289   $114.83   $114.85   $114.80  
  7 purchase totals = $1,199.53       $1,300.9944   $1,300.99   $1,301.00   $1,301.00