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 $184.57   8.562%   $200.3729   $200.37   $200.35   $200.40  
  Purchase #2 $199.93   13.189%   $226.2988   $226.30   $226.30   $226.30  
  Purchase #3 $76.47   3.534%   $79.1724   $79.17   $79.15   $79.20  
  Purchase #4 $69.76   4.330%   $72.7806   $72.78   $72.80   $72.80  
  Purchase #5 $145.61   3.497%   $150.702   $150.70   $150.70   $150.70  
  Purchase #6 $237.42   9.712%   $260.4782   $260.48   $260.50   $260.50  
  Purchase #7 $30.94   3.532%   $32.0328   $32.03   $32.05   $32.00  
  7 purchase totals = $944.70       $1,021.8377   $1,021.83   $1,021.85   $1,021.90