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 $209.87   12.360%   $235.8099   $235.81   $235.80   $235.80  
  Purchase #2 $110.31   3.244%   $113.8885   $113.89   $113.90   $113.90  
  Purchase #3 $117.66   10.625%   $130.1614   $130.16   $130.15   $130.20  
  Purchase #4 $214.92   3.237%   $221.877   $221.88   $221.90   $221.90  
  Purchase #5 $151.89   13.516%   $172.4195   $172.42   $172.40   $172.40  
  Purchase #6 $241.97   9.386%   $264.6813   $264.68   $264.70   $264.70  
  Purchase #7 $244.26   11.461%   $272.2546   $272.25   $272.25   $272.30  
  7 purchase totals = $1,290.88       $1,411.0922   $1,411.09   $1,411.10   $1,411.20