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 $30.68   6.530%   $32.6834   $32.68   $32.70   $32.70  
  Purchase #2 $24.59   6.763%   $26.253   $26.25   $26.25   $26.30  
  Purchase #3 $109.64   11.824%   $122.6038   $122.60   $122.60   $122.60  
  Purchase #4 $206.59   4.593%   $216.0787   $216.08   $216.10   $216.10  
  Purchase #5 $36.61   11.357%   $40.7678   $40.77   $40.75   $40.80  
  Purchase #6 $249.97   9.664%   $274.1271   $274.13   $274.15   $274.10  
  Purchase #7 $114.77   5.243%   $120.7874   $120.79   $120.80   $120.80  
  7 purchase totals = $772.85       $833.3012   $833.30   $833.35   $833.40