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 $88.70   8.276%   $96.0408   $96.04   $96.05   $96.00  
  Purchase #2 $186.43   13.266%   $211.1618   $211.16   $211.15   $211.20  
  Purchase #3 $76.94   13.394%   $87.2453   $87.25   $87.25   $87.20  
  Purchase #4 $230.64   10.839%   $255.6391   $255.64   $255.65   $255.60  
  Purchase #5 $149.80   4.375%   $156.3538   $156.35   $156.35   $156.40  
  Purchase #6 $16.81   9.126%   $18.3441   $18.34   $18.35   $18.30  
  Purchase #7 $130.58   5.562%   $137.8429   $137.84   $137.85   $137.80  
  7 purchase totals = $879.90       $962.6278   $962.62   $962.65   $962.50