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 $191.68   6.442%   $204.028   $204.03   $204.05   $204.00  
  Purchase #2 $32.89   7.213%   $35.2624   $35.26   $35.25   $35.30  
  Purchase #3 $66.76   3.803%   $69.2989   $69.30   $69.30   $69.30  
  Purchase #4 $106.52   6.823%   $113.7879   $113.79   $113.80   $113.80  
  Purchase #5 $55.92   11.470%   $62.334   $62.33   $62.35   $62.30  
  Purchase #6 $151.32   5.759%   $160.0345   $160.03   $160.05   $160.00  
  Purchase #7 $211.38   13.609%   $240.1467   $240.15   $240.15   $240.10  
  7 purchase totals = $816.47       $884.8924   $884.89   $884.95   $884.80