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 $232.75   13.710%   $264.66   $264.66   $264.65   $264.70  
  Purchase #2 $30.59   5.110%   $32.1531   $32.15   $32.15   $32.20  
  Purchase #3 $73.62   8.817%   $80.1111   $80.11   $80.10   $80.10  
  Purchase #4 $96.27   12.753%   $108.5473   $108.55   $108.55   $108.50  
  Purchase #5 $29.95   5.591%   $31.6245   $31.62   $31.60   $31.60  
  Purchase #6 $68.31   6.347%   $72.6456   $72.65   $72.65   $72.60  
  Purchase #7 $158.63   10.605%   $175.4527   $175.45   $175.45   $175.50  
  7 purchase totals = $690.12       $765.1943   $765.19   $765.15   $765.20