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 $118.92   4.522%   $124.2976   $124.30   $124.30   $124.30  
  Purchase #2 $227.28   3.320%   $234.8257   $234.83   $234.85   $234.80  
  Purchase #3 $66.48   8.459%   $72.1035   $72.10   $72.10   $72.10  
  Purchase #4 $234.35   3.228%   $241.9148   $241.91   $241.90   $241.90  
  Purchase #5 $225.43   4.593%   $235.784   $235.78   $235.80   $235.80  
  Purchase #6 $217.57   10.273%   $239.921   $239.92   $239.90   $239.90  
  Purchase #7 $105.43   12.675%   $118.7933   $118.79   $118.80   $118.80  
  7 purchase totals = $1,195.46       $1,267.6399   $1,267.63   $1,267.65   $1,267.60