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 $48.54   8.409%   $52.6217   $52.62   $52.60   $52.60  
  Purchase #2 $214.31   3.228%   $221.2279   $221.23   $221.25   $221.20  
  Purchase #3 $164.27   13.695%   $186.7668   $186.77   $186.75   $186.80  
  Purchase #4 $25.55   8.142%   $27.6303   $27.63   $27.65   $27.60  
  Purchase #5 $247.97   9.293%   $271.0139   $271.01   $271.00   $271.00  
  Purchase #6 $58.85   13.351%   $66.7071   $66.71   $66.70   $66.70  
  Purchase #7 $250.28   8.684%   $272.0143   $272.01   $272.00   $272.00  
  7 purchase totals = $1,009.77       $1,097.9820   $1,097.98   $1,097.95   $1,097.90