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 $90.31   5.865%   $95.6067   $95.61   $95.60   $95.60  
  Purchase #2 $204.51   8.244%   $221.3698   $221.37   $221.35   $221.40  
  Purchase #3 $91.94   4.441%   $96.0231   $96.02   $96.00   $96.00  
  Purchase #4 $192.25   4.788%   $201.4549   $201.45   $201.45   $201.50  
  Purchase #5 $57.32   7.727%   $61.7491   $61.75   $61.75   $61.70  
  Purchase #6 $184.35   13.254%   $208.7837   $208.78   $208.80   $208.80  
  Purchase #7 $122.38   13.523%   $138.9294   $138.93   $138.95   $138.90  
  7 purchase totals = $943.06       $1,023.9167   $1,023.91   $1,023.90   $1,023.90