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 $61.26   7.758%   $66.0126   $66.01   $66.00   $66.00  
  Purchase #2 $187.38   7.849%   $202.0875   $202.09   $202.10   $202.10  
  Purchase #3 $203.98   5.696%   $215.5987   $215.60   $215.60   $215.60  
  Purchase #4 $180.86   6.581%   $192.7624   $192.76   $192.75   $192.80  
  Purchase #5 $142.81   3.660%   $148.0368   $148.04   $148.05   $148.00  
  Purchase #6 $25.95   5.531%   $27.3853   $27.39   $27.40   $27.40  
  Purchase #7 $231.32   7.736%   $249.2149   $249.21   $249.20   $249.20  
  7 purchase totals = $1,033.56       $1,101.0982   $1,101.10   $1,101.10   $1,101.10