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 $146.85   12.548%   $165.2767   $165.28   $165.30   $165.30  
  Purchase #2 $82.57   6.128%   $87.6299   $87.63   $87.65   $87.60  
  Purchase #3 $84.69   11.556%   $94.4768   $94.48   $94.50   $94.50  
  Purchase #4 $69.84   12.477%   $78.5539   $78.55   $78.55   $78.60  
  Purchase #5 $145.94   6.699%   $155.7165   $155.72   $155.70   $155.70  
  Purchase #6 $206.69   13.703%   $235.0127   $235.01   $235.00   $235.00  
  Purchase #7 $139.76   5.728%   $147.7655   $147.77   $147.75   $147.80  
  7 purchase totals = $876.34       $964.4320   $964.44   $964.45   $964.50