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 $209.46   5.798%   $221.6045   $221.60   $221.60   $221.60  
  Purchase #2 $184.84   3.527%   $191.3593   $191.36   $191.35   $191.40  
  Purchase #3 $175.90   5.610%   $185.768   $185.77   $185.75   $185.80  
  Purchase #4 $45.86   4.220%   $47.7953   $47.80   $47.80   $47.80  
  Purchase #5 $123.76   10.238%   $136.4305   $136.43   $136.45   $136.40  
  Purchase #6 $43.90   5.232%   $46.1968   $46.20   $46.20   $46.20  
  Purchase #7 $211.26   11.466%   $235.4831   $235.48   $235.50   $235.50  
  7 purchase totals = $994.98       $1,064.6375   $1,064.64   $1,064.65   $1,064.70