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 $244.27   8.751%   $265.6461   $265.65   $265.65   $265.60  
  Purchase #2 $174.98   10.262%   $192.9364   $192.94   $192.95   $192.90  
  Purchase #3 $38.59   5.360%   $40.6584   $40.66   $40.65   $40.70  
  Purchase #4 $170.30   3.719%   $176.6335   $176.63   $176.65   $176.60  
  Purchase #5 $79.81   12.861%   $90.0744   $90.07   $90.05   $90.10  
  Purchase #6 $27.53   8.656%   $29.913   $29.91   $29.90   $29.90  
  Purchase #7 $149.39   4.620%   $156.2918   $156.29   $156.30   $156.30  
  7 purchase totals = $884.87       $952.1536   $952.15   $952.15   $952.10