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 $218.81   11.495%   $243.9622   $243.96   $243.95   $244.00  
  Purchase #2 $223.47   6.169%   $237.2559   $237.26   $237.25   $237.30  
  Purchase #3 $42.31   5.381%   $44.5867   $44.59   $44.60   $44.60  
  Purchase #4 $186.33   5.172%   $195.967   $195.97   $195.95   $196.00  
  Purchase #5 $22.61   10.180%   $24.9117   $24.91   $24.90   $24.90  
  Purchase #6 $183.79   6.328%   $195.4202   $195.42   $195.40   $195.40  
  Purchase #7 $229.66   4.121%   $239.1243   $239.12   $239.10   $239.10  
  7 purchase totals = $1,106.98       $1,181.2280   $1,181.23   $1,181.15   $1,181.30