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 $235.61   13.566%   $267.5729   $267.57   $267.55   $267.60  
  Purchase #2 $166.31   7.542%   $178.8531   $178.85   $178.85   $178.90  
  Purchase #3 $109.28   4.155%   $113.8206   $113.82   $113.80   $113.80  
  Purchase #4 $53.26   12.745%   $60.048   $60.05   $60.05   $60.00  
  Purchase #5 $107.69   10.442%   $118.935   $118.94   $118.95   $118.90  
  Purchase #6 $205.43   5.691%   $217.121   $217.12   $217.10   $217.10  
  Purchase #7 $239.32   5.122%   $251.578   $251.58   $251.60   $251.60  
  7 purchase totals = $1,116.90       $1,207.9286   $1,207.93   $1,207.90   $1,207.90