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 $206.58   7.351%   $221.7657   $221.77   $221.75   $221.80  
  Purchase #2 $148.50   10.434%   $163.9945   $163.99   $164.00   $164.00  
  Purchase #3 $44.60   4.769%   $46.727   $46.73   $46.75   $46.70  
  Purchase #4 $232.35   4.481%   $242.7616   $242.76   $242.75   $242.80  
  Purchase #5 $80.44   8.478%   $87.2597   $87.26   $87.25   $87.30  
  Purchase #6 $212.85   4.430%   $222.2793   $222.28   $222.30   $222.30  
  Purchase #7 $117.93   11.253%   $131.2007   $131.20   $131.20   $131.20  
  7 purchase totals = $1,043.25       $1,115.9885   $1,115.99   $1,116.00   $1,116.10