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 $184.76   12.624%   $208.0841   $208.08   $208.10   $208.10  
  Purchase #2 $64.65   11.490%   $72.0783   $72.08   $72.10   $72.10  
  Purchase #3 $201.29   11.549%   $224.537   $224.54   $224.55   $224.50  
  Purchase #4 $120.97   12.159%   $135.6787   $135.68   $135.70   $135.70  
  Purchase #5 $27.28   7.579%   $29.3476   $29.35   $29.35   $29.30  
  Purchase #6 $235.73   9.829%   $258.8999   $258.90   $258.90   $258.90  
  Purchase #7 $242.69   12.460%   $272.9292   $272.93   $272.95   $272.90  
  7 purchase totals = $1,077.37       $1,201.5548   $1,201.56   $1,201.65   $1,201.50