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 $50.72   6.752%   $54.1446   $54.14   $54.15   $54.10  
  Purchase #2 $115.93   9.453%   $126.8889   $126.89   $126.90   $126.90  
  Purchase #3 $195.60   8.682%   $212.582   $212.58   $212.60   $212.60  
  Purchase #4 $230.99   3.704%   $239.5459   $239.55   $239.55   $239.50  
  Purchase #5 $221.52   4.655%   $231.8318   $231.83   $231.85   $231.80  
  Purchase #6 $216.41   8.748%   $235.3415   $235.34   $235.35   $235.30  
  Purchase #7 $69.32   4.823%   $72.6633   $72.66   $72.65   $72.70  
  7 purchase totals = $1,100.49       $1,172.9980   $1,172.99   $1,173.05   $1,172.90