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 $208.30   12.851%   $235.0686   $235.07   $235.05   $235.10  
  Purchase #2 $151.51   3.432%   $156.7098   $156.71   $156.70   $156.70  
  Purchase #3 $112.96   12.329%   $126.8868   $126.89   $126.90   $126.90  
  Purchase #4 $173.29   8.213%   $187.5223   $187.52   $187.50   $187.50  
  Purchase #5 $247.97   4.203%   $258.3922   $258.39   $258.40   $258.40  
  Purchase #6 $95.79   13.529%   $108.7494   $108.75   $108.75   $108.70  
  Purchase #7 $111.40   8.238%   $120.5771   $120.58   $120.60   $120.60  
  7 purchase totals = $1,101.22       $1,193.9062   $1,193.91   $1,193.90   $1,193.90