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 $229.96   11.564%   $256.5526   $256.55   $256.55   $256.60  
  Purchase #2 $118.25   7.127%   $126.6777   $126.68   $126.70   $126.70  
  Purchase #3 $172.31   13.388%   $195.3789   $195.38   $195.40   $195.40  
  Purchase #4 $12.99   7.822%   $14.0061   $14.01   $14.00   $14.00  
  Purchase #5 $168.89   5.648%   $178.4289   $178.43   $178.45   $178.40  
  Purchase #6 $90.34   3.571%   $93.566   $93.57   $93.55   $93.60  
  Purchase #7 $84.55   13.250%   $95.7529   $95.75   $95.75   $95.80  
  7 purchase totals = $877.29       $960.3631   $960.37   $960.40   $960.50