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 $245.46   10.712%   $271.7537   $271.75   $271.75   $271.80  
  Purchase #2 $96.32   4.269%   $100.4319   $100.43   $100.45   $100.40  
  Purchase #3 $167.81   13.819%   $190.9997   $191.00   $191.00   $191.00  
  Purchase #4 $104.79   10.726%   $116.0298   $116.03   $116.05   $116.00  
  Purchase #5 $170.96   9.159%   $186.6182   $186.62   $186.60   $186.60  
  Purchase #6 $196.49   8.792%   $213.7654   $213.77   $213.75   $213.80  
  Purchase #7 $166.70   12.715%   $187.8959   $187.90   $187.90   $187.90  
  7 purchase totals = $1,148.53       $1,267.4946   $1,267.50   $1,267.50   $1,267.50