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 $89.85   3.295%   $92.8106   $92.81   $92.80   $92.80  
  Purchase #2 $23.46   3.832%   $24.359   $24.36   $24.35   $24.40  
  Purchase #3 $87.97   11.623%   $98.1948   $98.19   $98.20   $98.20  
  Purchase #4 $58.30   4.716%   $61.0494   $61.05   $61.05   $61.00  
  Purchase #5 $193.57   13.701%   $220.091   $220.09   $220.10   $220.10  
  Purchase #6 $129.29   5.607%   $136.5393   $136.54   $136.55   $136.50  
  Purchase #7 $164.48   3.505%   $170.245   $170.25   $170.25   $170.20  
  7 purchase totals = $746.92       $803.2891   $803.29   $803.30   $803.20