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 $208.45   11.543%   $232.5114   $232.51   $232.50   $232.50  
  Purchase #2 $148.69   8.303%   $161.0357   $161.04   $161.05   $161.00  
  Purchase #3 $247.98   7.571%   $266.7546   $266.75   $266.75   $266.80  
  Purchase #4 $199.92   9.229%   $218.3706   $218.37   $218.35   $218.40  
  Purchase #5 $133.45   6.318%   $141.8814   $141.88   $141.90   $141.90  
  Purchase #6 $188.42   13.574%   $213.9961   $214.00   $214.00   $214.00  
  Purchase #7 $165.33   13.148%   $187.0676   $187.07   $187.05   $187.10  
  7 purchase totals = $1,292.24       $1,421.6174   $1,421.62   $1,421.60   $1,421.70