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 $56.40   11.154%   $62.6909   $62.69   $62.70   $62.70  
  Purchase #2 $245.47   3.399%   $253.8135   $253.81   $253.80   $253.80  
  Purchase #3 $142.50   5.256%   $149.9898   $149.99   $150.00   $150.00  
  Purchase #4 $8.98   11.784%   $10.0382   $10.04   $10.05   $10.00  
  Purchase #5 $133.76   5.783%   $141.4953   $141.50   $141.50   $141.50  
  Purchase #6 $241.73   3.146%   $249.3348   $249.33   $249.35   $249.30  
  Purchase #7 $16.66   11.300%   $18.5426   $18.54   $18.55   $18.50  
  7 purchase totals = $845.50       $885.9051   $885.90   $885.95   $885.80