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 $209.70   11.107%   $232.9914   $232.99   $233.00   $233.00  
  Purchase #2 $137.96   4.839%   $144.6359   $144.64   $144.65   $144.60  
  Purchase #3 $116.39   9.689%   $127.667   $127.67   $127.65   $127.70  
  Purchase #4 $242.53   7.687%   $261.1733   $261.17   $261.15   $261.20  
  Purchase #5 $187.32   9.238%   $204.6246   $204.62   $204.60   $204.60  
  Purchase #6 $158.57   3.168%   $163.5935   $163.59   $163.60   $163.60  
  Purchase #7 $51.80   4.307%   $54.031   $54.03   $54.05   $54.00  
  7 purchase totals = $1,104.27       $1,188.7167   $1,188.71   $1,188.70   $1,188.70