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 $153.80   6.114%   $163.2033   $163.20   $163.20   $163.20  
  Purchase #2 $161.51   13.243%   $182.8988   $182.90   $182.90   $182.90  
  Purchase #3 $191.37   3.645%   $198.3454   $198.35   $198.35   $198.30  
  Purchase #4 $84.27   3.151%   $86.9253   $86.93   $86.95   $86.90  
  Purchase #5 $164.61   4.615%   $172.2068   $172.21   $172.20   $172.20  
  Purchase #6 $69.40   5.279%   $73.0636   $73.06   $73.05   $73.10  
  Purchase #7 $54.68   4.279%   $57.0198   $57.02   $57.00   $57.00  
  7 purchase totals = $879.64       $933.6630   $933.67   $933.65   $933.60