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 $222.83   5.319%   $234.6823   $234.68   $234.70   $234.70  
  Purchase #2 $157.26   12.497%   $176.9128   $176.91   $176.90   $176.90  
  Purchase #3 $197.89   6.412%   $210.5787   $210.58   $210.60   $210.60  
  Purchase #4 $13.65   6.184%   $14.4941   $14.49   $14.50   $14.50  
  Purchase #5 $230.37   3.243%   $237.8409   $237.84   $237.85   $237.80  
  Purchase #6 $47.45   12.192%   $53.2351   $53.24   $53.25   $53.20  
  Purchase #7 $74.59   11.559%   $83.2119   $83.21   $83.20   $83.20  
  7 purchase totals = $944.04       $1,010.9558   $1,010.95   $1,011.00   $1,010.90