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 $218.47   3.646%   $226.4354   $226.44   $226.45   $226.40  
  Purchase #2 $176.58   11.317%   $196.5636   $196.56   $196.55   $196.60  
  Purchase #3 $120.46   5.194%   $126.7167   $126.72   $126.70   $126.70  
  Purchase #4 $21.36   10.789%   $23.6645   $23.66   $23.65   $23.70  
  Purchase #5 $198.92   13.494%   $225.7623   $225.76   $225.75   $225.80  
  Purchase #6 $247.30   6.364%   $263.0382   $263.04   $263.05   $263.00  
  Purchase #7 $226.57   3.604%   $234.7356   $234.74   $234.75   $234.70  
  7 purchase totals = $1,209.66       $1,296.9163   $1,296.92   $1,296.90   $1,296.90