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 $118.69   5.410%   $125.1111   $125.11   $125.10   $125.10  
  Purchase #2 $170.30   9.636%   $186.7101   $186.71   $186.70   $186.70  
  Purchase #3 $236.55   12.736%   $266.677   $266.68   $266.70   $266.70  
  Purchase #4 $79.40   5.293%   $83.6026   $83.60   $83.60   $83.60  
  Purchase #5 $10.95   12.186%   $12.2844   $12.28   $12.30   $12.30  
  Purchase #6 $233.89   5.424%   $246.5762   $246.58   $246.60   $246.60  
  Purchase #7 $27.71   10.477%   $30.6132   $30.61   $30.60   $30.60  
  7 purchase totals = $877.49       $951.5746   $951.57   $951.60   $951.60