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 $86.79   11.640%   $96.8924   $96.89   $96.90   $96.90  
  Purchase #2 $205.88   12.167%   $230.9294   $230.93   $230.95   $230.90  
  Purchase #3 $106.35   6.825%   $113.6084   $113.61   $113.60   $113.60  
  Purchase #4 $233.58   10.759%   $258.7109   $258.71   $258.70   $258.70  
  Purchase #5 $48.61   8.361%   $52.6743   $52.67   $52.65   $52.70  
  Purchase #6 $114.61   11.344%   $127.6114   $127.61   $127.60   $127.60  
  Purchase #7 $119.46   5.460%   $125.9825   $125.98   $126.00   $126.00  
  7 purchase totals = $915.28       $1,006.4093   $1,006.40   $1,006.40   $1,006.40