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 $150.46   7.588%   $161.8769   $161.88   $161.90   $161.90  
  Purchase #2 $78.84   9.131%   $86.0389   $86.04   $86.05   $86.00  
  Purchase #3 $45.58   10.744%   $50.4771   $50.48   $50.50   $50.50  
  Purchase #4 $68.26   11.394%   $76.0375   $76.04   $76.05   $76.00  
  Purchase #5 $229.97   6.731%   $245.4493   $245.45   $245.45   $245.40  
  Purchase #6 $56.63   11.345%   $63.0547   $63.05   $63.05   $63.10  
  Purchase #7 $36.49   8.576%   $39.6194   $39.62   $39.60   $39.60  
  7 purchase totals = $666.23       $722.5538   $722.56   $722.60   $722.50