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 $113.88   9.554%   $124.7601   $124.76   $124.75   $124.80  
  Purchase #2 $83.69   6.396%   $89.0428   $89.04   $89.05   $89.00  
  Purchase #3 $231.85   3.156%   $239.1672   $239.17   $239.15   $239.20  
  Purchase #4 $111.76   9.169%   $122.0073   $122.01   $122.00   $122.00  
  Purchase #5 $25.37   3.682%   $26.3041   $26.30   $26.30   $26.30  
  Purchase #6 $220.47   6.816%   $235.4972   $235.50   $235.50   $235.50  
  Purchase #7 $215.40   5.293%   $226.8011   $226.80   $226.80   $226.80  
  7 purchase totals = $1,002.42       $1,063.5798   $1,063.58   $1,063.55   $1,063.60