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 $91.34   5.395%   $96.2678   $96.27   $96.25   $96.30  
  Purchase #2 $180.25   9.455%   $197.2926   $197.29   $197.30   $197.30  
  Purchase #3 $53.47   7.300%   $57.3733   $57.37   $57.35   $57.40  
  Purchase #4 $71.64   11.725%   $80.0398   $80.04   $80.05   $80.00  
  Purchase #5 $149.60   9.315%   $163.5352   $163.54   $163.55   $163.50  
  Purchase #6 $202.36   3.176%   $208.787   $208.79   $208.80   $208.80  
  Purchase #7 $149.60   4.255%   $155.9655   $155.97   $155.95   $156.00  
  7 purchase totals = $898.26       $959.2612   $959.27   $959.25   $959.30