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 $239.33   9.825%   $262.8442   $262.84   $262.85   $262.80  
  Purchase #2 $127.83   11.645%   $142.7158   $142.72   $142.70   $142.70  
  Purchase #3 $52.98   7.572%   $56.9916   $56.99   $57.00   $57.00  
  Purchase #4 $26.27   11.181%   $29.2072   $29.21   $29.20   $29.20  
  Purchase #5 $59.28   5.687%   $62.6513   $62.65   $62.65   $62.70  
  Purchase #6 $202.57   7.259%   $217.2746   $217.27   $217.25   $217.30  
  Purchase #7 $176.68   6.824%   $188.7366   $188.74   $188.75   $188.70  
  7 purchase totals = $884.94       $960.4213   $960.42   $960.40   $960.40