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 $55.93   5.862%   $59.2086   $59.21   $59.20   $59.20  
  Purchase #2 $173.36   8.441%   $187.9933   $187.99   $188.00   $188.00  
  Purchase #3 $48.27   5.798%   $51.0687   $51.07   $51.05   $51.10  
  Purchase #4 $72.98   12.691%   $82.2419   $82.24   $82.25   $82.20  
  Purchase #5 $148.67   4.245%   $154.981   $154.98   $155.00   $155.00  
  Purchase #6 $22.69   5.678%   $23.9783   $23.98   $24.00   $24.00  
  Purchase #7 $203.41   10.805%   $225.3885   $225.39   $225.40   $225.40  
  7 purchase totals = $725.31       $784.8603   $784.86   $784.90   $784.90