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 $73.45   5.861%   $77.7549   $77.75   $77.75   $77.80  
  Purchase #2 $171.40   12.666%   $193.1095   $193.11   $193.10   $193.10  
  Purchase #3 $125.65   7.710%   $135.3376   $135.34   $135.35   $135.30  
  Purchase #4 $46.26   6.516%   $49.2743   $49.27   $49.25   $49.30  
  Purchase #5 $182.83   6.240%   $194.2386   $194.24   $194.25   $194.20  
  Purchase #6 $185.76   6.202%   $197.2808   $197.28   $197.30   $197.30  
  Purchase #7 $191.71   12.512%   $215.6968   $215.70   $215.70   $215.70  
  7 purchase totals = $977.06       $1,062.6925   $1,062.69   $1,062.70   $1,062.70