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 $97.75   8.644%   $106.1995   $106.20   $106.20   $106.20  
  Purchase #2 $128.51   6.771%   $137.2114   $137.21   $137.20   $137.20  
  Purchase #3 $187.86   13.311%   $212.866   $212.87   $212.85   $212.90  
  Purchase #4 $97.93   5.116%   $102.9401   $102.94   $102.95   $102.90  
  Purchase #5 $11.97   12.324%   $13.4452   $13.45   $13.45   $13.40  
  Purchase #6 $116.37   13.440%   $132.0101   $132.01   $132.00   $132.00  
  Purchase #7 $246.54   12.789%   $278.07   $278.07   $278.05   $278.10  
  7 purchase totals = $886.93       $982.7423   $982.75   $982.70   $982.70