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 $33.52   8.407%   $36.338   $36.34   $36.35   $36.30  
  Purchase #2 $209.34   10.859%   $232.0722   $232.07   $232.05   $232.10  
  Purchase #3 $230.45   8.778%   $250.6789   $250.68   $250.70   $250.70  
  Purchase #4 $231.96   8.375%   $251.3867   $251.39   $251.40   $251.40  
  Purchase #5 $225.34   4.858%   $236.287   $236.29   $236.30   $236.30  
  Purchase #6 $245.91   8.373%   $266.5   $266.50   $266.50   $266.50  
  Purchase #7 $82.97   3.676%   $86.02   $86.02   $86.00   $86.00  
  7 purchase totals = $1,259.49       $1,359.2828   $1,359.29   $1,359.30   $1,359.30