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 $237.27   9.431%   $259.6469   $259.65   $259.65   $259.60  
  Purchase #2 $18.77   7.837%   $20.241   $20.24   $20.25   $20.20  
  Purchase #3 $60.94   6.465%   $64.8798   $64.88   $64.90   $64.90  
  Purchase #4 $230.29   8.370%   $249.5653   $249.57   $249.55   $249.60  
  Purchase #5 $178.28   8.149%   $192.808   $192.81   $192.80   $192.80  
  Purchase #6 $95.55   6.286%   $101.5563   $101.56   $101.55   $101.60  
  Purchase #7 $124.28   11.119%   $138.0987   $138.10   $138.10   $138.10  
  7 purchase totals = $945.38       $1,026.7960   $1,026.81   $1,026.80   $1,026.80