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 $244.81   12.534%   $275.4945   $275.49   $275.50   $275.50  
  Purchase #2 $58.65   4.121%   $61.067   $61.07   $61.05   $61.10  
  Purchase #3 $193.59   13.222%   $219.1865   $219.19   $219.20   $219.20  
  Purchase #4 $200.41   7.323%   $215.086   $215.09   $215.10   $215.10  
  Purchase #5 $240.26   13.230%   $272.0464   $272.05   $272.05   $272.00  
  Purchase #6 $235.81   13.601%   $267.8825   $267.88   $267.90   $267.90  
  Purchase #7 $113.77   4.535%   $118.9295   $118.93   $118.95   $118.90  
  7 purchase totals = $1,287.30       $1,429.6924   $1,429.70   $1,429.75   $1,429.70