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 $241.30   4.683%   $252.6001   $252.60   $252.60   $252.60  
  Purchase #2 $44.57   6.393%   $47.4194   $47.42   $47.40   $47.40  
  Purchase #3 $92.84   13.603%   $105.469   $105.47   $105.45   $105.50  
  Purchase #4 $243.89   5.444%   $257.1674   $257.17   $257.15   $257.20  
  Purchase #5 $186.25   4.124%   $193.931   $193.93   $193.95   $193.90  
  Purchase #6 $108.85   6.591%   $116.0243   $116.02   $116.00   $116.00  
  Purchase #7 $41.39   6.521%   $44.089   $44.09   $44.10   $44.10  
  7 purchase totals = $959.09       $1,016.7002   $1,016.70   $1,016.65   $1,016.70