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 $167.59   6.756%   $178.9124   $178.91   $178.90   $178.90  
  Purchase #2 $246.42   6.320%   $261.9937   $261.99   $262.00   $262.00  
  Purchase #3 $71.55   7.318%   $76.786   $76.79   $76.80   $76.80  
  Purchase #4 $48.51   11.536%   $54.1061   $54.11   $54.10   $54.10  
  Purchase #5 $187.65   10.144%   $206.6852   $206.69   $206.70   $206.70  
  Purchase #6 $97.79   6.676%   $104.3185   $104.32   $104.30   $104.30  
  Purchase #7 $169.67   5.824%   $179.5516   $179.55   $179.55   $179.60  
  7 purchase totals = $989.18       $1,062.3535   $1,062.36   $1,062.35   $1,062.40