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 $113.80   12.648%   $128.1934   $128.19   $128.20   $128.20  
  Purchase #2 $166.93   7.186%   $178.9256   $178.93   $178.95   $178.90  
  Purchase #3 $227.49   3.624%   $235.7342   $235.73   $235.75   $235.70  
  Purchase #4 $213.43   8.646%   $231.8832   $231.88   $231.90   $231.90  
  Purchase #5 $151.83   3.388%   $156.974   $156.97   $156.95   $157.00  
  Purchase #6 $208.43   6.257%   $221.4715   $221.47   $221.45   $221.50  
  Purchase #7 $113.45   11.441%   $126.4298   $126.43   $126.45   $126.40  
  7 purchase totals = $1,195.36       $1,279.6117   $1,279.60   $1,279.65   $1,279.60