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 $44.37   13.859%   $50.5192   $50.52   $50.50   $50.50  
  Purchase #2 $119.57   5.488%   $126.132   $126.13   $126.15   $126.10  
  Purchase #3 $29.40   11.594%   $32.8086   $32.81   $32.80   $32.80  
  Purchase #4 $104.85   8.806%   $114.0831   $114.08   $114.10   $114.10  
  Purchase #5 $221.66   6.227%   $235.4628   $235.46   $235.45   $235.50  
  Purchase #6 $233.54   12.395%   $262.4873   $262.49   $262.50   $262.50  
  Purchase #7 $174.99   10.850%   $193.9764   $193.98   $194.00   $194.00  
  7 purchase totals = $928.38       $1,015.4694   $1,015.47   $1,015.50   $1,015.50