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 $54.65   12.440%   $61.4485   $61.45   $61.45   $61.40  
  Purchase #2 $198.26   4.213%   $206.6127   $206.61   $206.60   $206.60  
  Purchase #3 $148.48   5.693%   $156.933   $156.93   $156.95   $156.90  
  Purchase #4 $239.81   6.676%   $255.8197   $255.82   $255.80   $255.80  
  Purchase #5 $30.38   7.429%   $32.6369   $32.64   $32.65   $32.60  
  Purchase #6 $209.98   10.395%   $231.8074   $231.81   $231.80   $231.80  
  Purchase #7 $232.73   7.253%   $249.6099   $249.61   $249.60   $249.60  
  7 purchase totals = $1,114.29       $1,194.8681   $1,194.87   $1,194.85   $1,194.70