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 $244.53   10.102%   $269.2324   $269.23   $269.25   $269.20  
  Purchase #2 $55.80   10.603%   $61.7165   $61.72   $61.70   $61.70  
  Purchase #3 $47.49   8.518%   $51.5352   $51.54   $51.55   $51.50  
  Purchase #4 $117.92   9.574%   $129.2097   $129.21   $129.20   $129.20  
  Purchase #5 $199.33   12.584%   $224.4137   $224.41   $224.40   $224.40  
  Purchase #6 $249.64   5.211%   $262.6487   $262.65   $262.65   $262.60  
  Purchase #7 $45.38   11.349%   $50.5302   $50.53   $50.55   $50.50  
  7 purchase totals = $960.09       $1,049.2864   $1,049.29   $1,049.30   $1,049.10