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 $247.89   7.831%   $267.3023   $267.30   $267.30   $267.30  
  Purchase #2 $175.26   8.624%   $190.3744   $190.37   $190.35   $190.40  
  Purchase #3 $26.59   7.639%   $28.6212   $28.62   $28.60   $28.60  
  Purchase #4 $92.29   4.774%   $96.6959   $96.70   $96.70   $96.70  
  Purchase #5 $236.75   13.233%   $268.0791   $268.08   $268.10   $268.10  
  Purchase #6 $97.51   6.380%   $103.7311   $103.73   $103.75   $103.70  
  Purchase #7 $72.77   8.321%   $78.8252   $78.83   $78.85   $78.80  
  7 purchase totals = $949.06       $1,033.6292   $1,033.63   $1,033.65   $1,033.60