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 $247.74   7.110%   $265.3543   $265.35   $265.35   $265.40  
  Purchase #2 $167.55   3.402%   $173.2501   $173.25   $173.25   $173.30  
  Purchase #3 $160.44   6.408%   $170.721   $170.72   $170.70   $170.70  
  Purchase #4 $235.62   3.439%   $243.723   $243.72   $243.70   $243.70  
  Purchase #5 $34.54   10.550%   $38.184   $38.18   $38.20   $38.20  
  Purchase #6 $165.36   13.851%   $188.264   $188.26   $188.25   $188.30  
  Purchase #7 $245.48   9.333%   $268.3906   $268.39   $268.40   $268.40  
  7 purchase totals = $1,256.73       $1,347.8870   $1,347.87   $1,347.85   $1,348.00