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 $76.73   10.389%   $84.7015   $84.70   $84.70   $84.70  
  Purchase #2 $55.93   10.152%   $61.608   $61.61   $61.60   $61.60  
  Purchase #3 $9.80   11.256%   $10.9031   $10.90   $10.90   $10.90  
  Purchase #4 $230.64   3.846%   $239.5104   $239.51   $239.50   $239.50  
  Purchase #5 $244.83   10.762%   $271.1786   $271.18   $271.20   $271.20  
  Purchase #6 $244.58   13.170%   $276.7912   $276.79   $276.80   $276.80  
  Purchase #7 $238.54   8.760%   $259.4361   $259.44   $259.45   $259.40  
  7 purchase totals = $1,101.05       $1,204.1289   $1,204.13   $1,204.15   $1,204.10