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 $229.54   10.544%   $253.7427   $253.74   $253.75   $253.70  
  Purchase #2 $190.55   13.502%   $216.2781   $216.28   $216.30   $216.30  
  Purchase #3 $55.35   4.348%   $57.7566   $57.76   $57.75   $57.80  
  Purchase #4 $123.34   5.789%   $130.4802   $130.48   $130.50   $130.50  
  Purchase #5 $72.88   8.679%   $79.2053   $79.21   $79.20   $79.20  
  Purchase #6 $92.78   8.247%   $100.4316   $100.43   $100.45   $100.40  
  Purchase #7 $22.47   6.322%   $23.8906   $23.89   $23.90   $23.90  
  7 purchase totals = $786.91       $861.7851   $861.79   $861.85   $861.80