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 $238.65   11.270%   $265.5459   $265.55   $265.55   $265.50  
  Purchase #2 $142.83   7.605%   $153.6922   $153.69   $153.70   $153.70  
  Purchase #3 $48.85   4.203%   $50.9032   $50.90   $50.90   $50.90  
  Purchase #4 $221.92   10.108%   $244.3517   $244.35   $244.35   $244.40  
  Purchase #5 $42.82   12.669%   $48.2449   $48.24   $48.25   $48.20  
  Purchase #6 $49.84   4.425%   $52.0454   $52.05   $52.05   $52.00  
  Purchase #7 $231.70   5.560%   $244.5825   $244.58   $244.60   $244.60  
  7 purchase totals = $976.61       $1,059.3658   $1,059.36   $1,059.40   $1,059.30