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 $179.44   10.322%   $197.9618   $197.96   $197.95   $198.00  
  Purchase #2 $39.75   6.493%   $42.331   $42.33   $42.35   $42.30  
  Purchase #3 $73.75   8.367%   $79.9207   $79.92   $79.90   $79.90  
  Purchase #4 $183.88   5.748%   $194.4494   $194.45   $194.45   $194.40  
  Purchase #5 $105.97   13.683%   $120.4699   $120.47   $120.45   $120.50  
  Purchase #6 $114.59   8.506%   $124.337   $124.34   $124.35   $124.30  
  Purchase #7 $115.51   5.181%   $121.4946   $121.49   $121.50   $121.50  
  7 purchase totals = $812.89       $880.9644   $880.96   $880.95   $880.90