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 $224.54   10.847%   $248.8959   $248.90   $248.90   $248.90  
  Purchase #2 $32.94   6.173%   $34.9734   $34.97   $34.95   $35.00  
  Purchase #3 $107.68   4.710%   $112.7517   $112.75   $112.75   $112.80  
  Purchase #4 $210.94   7.508%   $226.7774   $226.78   $226.80   $226.80  
  Purchase #5 $31.81   5.761%   $33.6426   $33.64   $33.65   $33.60  
  Purchase #6 $161.40   7.246%   $173.095   $173.10   $173.10   $173.10  
  Purchase #7 $220.44   12.103%   $247.1199   $247.12   $247.10   $247.10  
  7 purchase totals = $989.75       $1,077.2559   $1,077.26   $1,077.25   $1,077.30