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 $65.38   9.819%   $71.7997   $71.80   $71.80   $71.80  
  Purchase #2 $38.50   5.573%   $40.6456   $40.65   $40.65   $40.60  
  Purchase #3 $18.56   6.544%   $19.7746   $19.77   $19.75   $19.80  
  Purchase #4 $164.27   6.783%   $175.4124   $175.41   $175.40   $175.40  
  Purchase #5 $184.89   8.859%   $201.2694   $201.27   $201.25   $201.30  
  Purchase #6 $245.77   9.814%   $269.8899   $269.89   $269.90   $269.90  
  Purchase #7 $235.75   4.183%   $245.6114   $245.61   $245.60   $245.60  
  7 purchase totals = $953.12       $1,024.4030   $1,024.40   $1,024.35   $1,024.40