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 $52.66   12.649%   $59.321   $59.32   $59.30   $59.30  
  Purchase #2 $117.58   13.872%   $133.8907   $133.89   $133.90   $133.90  
  Purchase #3 $141.29   13.764%   $160.7372   $160.74   $160.75   $160.70  
  Purchase #4 $136.44   4.581%   $142.6903   $142.69   $142.70   $142.70  
  Purchase #5 $105.90   11.253%   $117.8169   $117.82   $117.80   $117.80  
  Purchase #6 $76.77   6.805%   $81.9942   $81.99   $82.00   $82.00  
  Purchase #7 $197.44   10.586%   $218.341   $218.34   $218.35   $218.30  
  7 purchase totals = $828.08       $914.7913   $914.79   $914.80   $914.70