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 $236.69   10.471%   $261.4738   $261.47   $261.45   $261.50  
  Purchase #2 $216.93   4.369%   $226.4077   $226.41   $226.40   $226.40  
  Purchase #3 $34.52   4.534%   $36.0851   $36.09   $36.10   $36.10  
  Purchase #4 $152.29   4.666%   $159.3959   $159.40   $159.40   $159.40  
  Purchase #5 $227.33   8.772%   $247.2714   $247.27   $247.25   $247.30  
  Purchase #6 $185.88   10.521%   $205.4364   $205.44   $205.45   $205.40  
  Purchase #7 $93.66   6.780%   $100.0101   $100.01   $100.00   $100.00  
  7 purchase totals = $1,147.30       $1,236.0804   $1,236.09   $1,236.05   $1,236.10