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 $32.85   3.677%   $34.0579   $34.06   $34.05   $34.10  
  Purchase #2 $96.96   4.324%   $101.1526   $101.15   $101.15   $101.20  
  Purchase #3 $117.36   4.693%   $122.8677   $122.87   $122.85   $122.90  
  Purchase #4 $90.81   5.725%   $96.0089   $96.01   $96.00   $96.00  
  Purchase #5 $51.93   10.224%   $57.2393   $57.24   $57.25   $57.20  
  Purchase #6 $111.95   9.507%   $122.5931   $122.59   $122.60   $122.60  
  Purchase #7 $194.57   5.430%   $205.1352   $205.14   $205.15   $205.10  
  7 purchase totals = $696.43       $739.0547   $739.06   $739.05   $739.10