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 $118.27   4.193%   $123.2291   $123.23   $123.25   $123.20  
  Purchase #2 $223.53   10.851%   $247.7852   $247.79   $247.80   $247.80  
  Purchase #3 $23.67   8.833%   $25.7608   $25.76   $25.75   $25.80  
  Purchase #4 $60.72   9.137%   $66.268   $66.27   $66.25   $66.30  
  Purchase #5 $250.80   7.621%   $269.9135   $269.91   $269.90   $269.90  
  Purchase #6 $203.30   8.750%   $221.0888   $221.09   $221.10   $221.10  
  Purchase #7 $67.51   6.773%   $72.0825   $72.08   $72.10   $72.10  
  7 purchase totals = $947.80       $1,026.1279   $1,026.13   $1,026.15   $1,026.20