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 $92.44   3.501%   $95.6763   $95.68   $95.70   $95.70  
  Purchase #2 $178.75   4.822%   $187.3693   $187.37   $187.35   $187.40  
  Purchase #3 $216.95   5.243%   $228.3247   $228.32   $228.30   $228.30  
  Purchase #4 $129.72   8.704%   $141.0108   $141.01   $141.00   $141.00  
  Purchase #5 $130.25   5.105%   $136.8993   $136.90   $136.90   $136.90  
  Purchase #6 $153.33   13.696%   $174.3301   $174.33   $174.35   $174.30  
  Purchase #7 $14.83   13.815%   $16.8788   $16.88   $16.90   $16.90  
  7 purchase totals = $916.27       $980.4893   $980.49   $980.50   $980.50