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 $90.61   7.307%   $97.2309   $97.23   $97.25   $97.20  
  Purchase #2 $33.94   6.406%   $36.1142   $36.11   $36.10   $36.10  
  Purchase #3 $208.72   5.734%   $220.688   $220.69   $220.70   $220.70  
  Purchase #4 $138.92   9.633%   $152.3022   $152.30   $152.30   $152.30  
  Purchase #5 $222.26   5.145%   $233.6953   $233.70   $233.70   $233.70  
  Purchase #6 $112.70   10.569%   $124.6113   $124.61   $124.60   $124.60  
  Purchase #7 $235.85   6.442%   $251.0435   $251.04   $251.05   $251.00  
  7 purchase totals = $1,043.00       $1,115.6854   $1,115.68   $1,115.70   $1,115.60