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 $153.95   5.232%   $162.0047   $162.00   $162.00   $162.00  
  Purchase #2 $44.57   8.137%   $48.1967   $48.20   $48.20   $48.20  
  Purchase #3 $83.82   5.835%   $88.7109   $88.71   $88.70   $88.70  
  Purchase #4 $214.72   11.326%   $239.0392   $239.04   $239.05   $239.00  
  Purchase #5 $56.87   11.813%   $63.5881   $63.59   $63.60   $63.60  
  Purchase #6 $130.85   6.423%   $139.2545   $139.25   $139.25   $139.30  
  Purchase #7 $57.94   9.479%   $63.4321   $63.43   $63.45   $63.40  
  7 purchase totals = $742.72       $804.2262   $804.22   $804.25   $804.20