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 $244.91   7.517%   $263.3199   $263.32   $263.30   $263.30  
  Purchase #2 $217.55   12.438%   $244.6089   $244.61   $244.60   $244.60  
  Purchase #3 $134.26   12.212%   $150.6558   $150.66   $150.65   $150.70  
  Purchase #4 $24.62   6.646%   $26.2562   $26.26   $26.25   $26.30  
  Purchase #5 $245.88   13.311%   $278.6091   $278.61   $278.60   $278.60  
  Purchase #6 $217.92   4.429%   $227.5717   $227.57   $227.55   $227.60  
  Purchase #7 $124.33   13.195%   $140.7353   $140.74   $140.75   $140.70  
  7 purchase totals = $1,209.47       $1,331.7569   $1,331.77   $1,331.70   $1,331.80