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 $204.81   4.177%   $213.3649   $213.36   $213.35   $213.40  
  Purchase #2 $198.89   4.117%   $207.0783   $207.08   $207.10   $207.10  
  Purchase #3 $242.52   13.866%   $276.1478   $276.15   $276.15   $276.10  
  Purchase #4 $40.95   10.789%   $45.3681   $45.37   $45.35   $45.40  
  Purchase #5 $162.53   12.608%   $183.0218   $183.02   $183.00   $183.00  
  Purchase #6 $21.85   3.107%   $22.5289   $22.53   $22.55   $22.50  
  Purchase #7 $115.32   3.733%   $119.6249   $119.62   $119.60   $119.60  
  7 purchase totals = $986.87       $1,067.1347   $1,067.13   $1,067.10   $1,067.10