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 $238.50   11.480%   $265.8798   $265.88   $265.90   $265.90  
  Purchase #2 $101.42   12.400%   $113.9961   $114.00   $114.00   $114.00  
  Purchase #3 $41.43   11.540%   $46.211   $46.21   $46.20   $46.20  
  Purchase #4 $105.31   7.558%   $113.2693   $113.27   $113.25   $113.30  
  Purchase #5 $92.33   4.493%   $96.4784   $96.48   $96.50   $96.50  
  Purchase #6 $49.58   12.114%   $55.5861   $55.59   $55.60   $55.60  
  Purchase #7 $160.28   4.620%   $167.6849   $167.68   $167.70   $167.70  
  7 purchase totals = $788.85       $859.1056   $859.11   $859.15   $859.20