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 $34.83   6.117%   $36.9606   $36.96   $36.95   $37.00  
  Purchase #2 $172.73   13.291%   $195.6875   $195.69   $195.70   $195.70  
  Purchase #3 $111.42   7.784%   $120.0929   $120.09   $120.10   $120.10  
  Purchase #4 $157.31   9.660%   $172.5061   $172.51   $172.50   $172.50  
  Purchase #5 $206.26   7.351%   $221.4222   $221.42   $221.40   $221.40  
  Purchase #6 $239.32   5.779%   $253.1503   $253.15   $253.15   $253.20  
  Purchase #7 $203.69   13.745%   $231.6872   $231.69   $231.70   $231.70  
  7 purchase totals = $1,125.56       $1,231.5068   $1,231.51   $1,231.50   $1,231.60