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 $39.74   8.235%   $43.0126   $43.01   $43.00   $43.00  
  Purchase #2 $182.38   7.853%   $196.7023   $196.70   $196.70   $196.70  
  Purchase #3 $50.31   3.392%   $52.0165   $52.02   $52.00   $52.00  
  Purchase #4 $94.63   3.808%   $98.2335   $98.23   $98.25   $98.20  
  Purchase #5 $169.83   11.528%   $189.408   $189.41   $189.40   $189.40  
  Purchase #6 $25.58   7.791%   $27.5729   $27.57   $27.55   $27.60  
  Purchase #7 $8.29   8.395%   $8.9859   $8.99   $9.00   $9.00  
  7 purchase totals = $570.76       $615.9317   $615.93   $615.90   $615.90