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 $225.29   3.723%   $233.6775   $233.68   $233.70   $233.70  
  Purchase #2 $24.97   11.173%   $27.7599   $27.76   $27.75   $27.80  
  Purchase #3 $81.77   13.695%   $92.9684   $92.97   $92.95   $93.00  
  Purchase #4 $69.69   3.311%   $71.9974   $72.00   $72.00   $72.00  
  Purchase #5 $156.81   9.206%   $171.2459   $171.25   $171.25   $171.20  
  Purchase #6 $34.90   5.666%   $36.8774   $36.88   $36.90   $36.90  
  Purchase #7 $208.93   12.249%   $234.5218   $234.52   $234.50   $234.50  
  7 purchase totals = $802.36       $869.0483   $869.06   $869.05   $869.10