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 $132.75   5.408%   $139.9291   $139.93   $139.95   $139.90  
  Purchase #2 $103.30   7.209%   $110.7469   $110.75   $110.75   $110.70  
  Purchase #3 $12.62   10.251%   $13.9137   $13.91   $13.90   $13.90  
  Purchase #4 $40.25   10.680%   $44.5487   $44.55   $44.55   $44.50  
  Purchase #5 $17.69   7.394%   $18.998   $19.00   $19.00   $19.00  
  Purchase #6 $36.77   7.483%   $39.5215   $39.52   $39.50   $39.50  
  Purchase #7 $20.66   13.264%   $23.4003   $23.40   $23.40   $23.40  
  7 purchase totals = $364.04       $391.0582   $391.06   $391.05   $390.90