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 $248.72   8.259%   $269.2618   $269.26   $269.25   $269.30  
  Purchase #2 $237.67   7.824%   $256.2653   $256.27   $256.25   $256.30  
  Purchase #3 $88.98   6.589%   $94.8429   $94.84   $94.85   $94.80  
  Purchase #4 $72.32   5.831%   $76.537   $76.54   $76.55   $76.50  
  Purchase #5 $231.27   4.102%   $240.7567   $240.76   $240.75   $240.80  
  Purchase #6 $59.77   11.785%   $66.8139   $66.81   $66.80   $66.80  
  Purchase #7 $63.74   7.600%   $68.5842   $68.58   $68.60   $68.60  
  7 purchase totals = $1,002.47       $1,073.0618   $1,073.06   $1,073.05   $1,073.10