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 $72.55   11.658%   $81.0079   $81.01   $81.00   $81.00  
  Purchase #2 $191.99   6.562%   $204.5884   $204.59   $204.60   $204.60  
  Purchase #3 $24.63   6.613%   $26.2588   $26.26   $26.25   $26.30  
  Purchase #4 $231.75   5.723%   $245.0131   $245.01   $245.00   $245.00  
  Purchase #5 $89.45   7.194%   $95.885   $95.89   $95.90   $95.90  
  Purchase #6 $86.61   6.382%   $92.1375   $92.14   $92.15   $92.10  
  Purchase #7 $231.55   11.637%   $258.4955   $258.50   $258.50   $258.50  
  7 purchase totals = $928.53       $1,003.3862   $1,003.40   $1,003.40   $1,003.40