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 $238.78   11.702%   $266.722   $266.72   $266.70   $266.70  
  Purchase #2 $42.72   13.704%   $48.5743   $48.57   $48.55   $48.60  
  Purchase #3 $123.64   5.216%   $130.0891   $130.09   $130.10   $130.10  
  Purchase #4 $169.88   3.216%   $175.3433   $175.34   $175.35   $175.30  
  Purchase #5 $247.29   3.492%   $255.9254   $255.93   $255.95   $255.90  
  Purchase #6 $115.47   6.212%   $122.643   $122.64   $122.65   $122.60  
  Purchase #7 $47.86   3.463%   $49.5174   $49.52   $49.50   $49.50  
  7 purchase totals = $985.64       $1,048.8145   $1,048.81   $1,048.80   $1,048.70