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 $238.59   3.181%   $246.1795   $246.18   $246.20   $246.20  
  Purchase #2 $78.34   6.143%   $83.1524   $83.15   $83.15   $83.20  
  Purchase #3 $214.61   11.865%   $240.0735   $240.07   $240.05   $240.10  
  Purchase #4 $207.27   4.464%   $216.5225   $216.52   $216.50   $216.50  
  Purchase #5 $163.79   5.104%   $172.1498   $172.15   $172.15   $172.10  
  Purchase #6 $139.26   12.839%   $157.1396   $157.14   $157.15   $157.10  
  Purchase #7 $183.87   5.512%   $194.0049   $194.00   $194.00   $194.00  
  7 purchase totals = $1,225.73       $1,309.2222   $1,309.21   $1,309.20   $1,309.20