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 $60.43   9.206%   $65.9932   $65.99   $66.00   $66.00  
  Purchase #2 $75.54   5.692%   $79.8397   $79.84   $79.85   $79.80  
  Purchase #3 $208.38   10.797%   $230.8788   $230.88   $230.90   $230.90  
  Purchase #4 $131.64   11.792%   $147.163   $147.16   $147.15   $147.20  
  Purchase #5 $168.93   6.344%   $179.6469   $179.65   $179.65   $179.60  
  Purchase #6 $148.33   10.733%   $164.2503   $164.25   $164.25   $164.30  
  Purchase #7 $131.49   12.616%   $148.0788   $148.08   $148.10   $148.10  
  7 purchase totals = $924.74       $1,015.8507   $1,015.85   $1,015.90   $1,015.90