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 $9.92   11.389%   $11.0498   $11.05   $11.05   $11.00  
  Purchase #2 $169.61   13.755%   $192.9399   $192.94   $192.95   $192.90  
  Purchase #3 $223.65   12.598%   $251.8254   $251.83   $251.85   $251.80  
  Purchase #4 $210.64   13.826%   $239.7631   $239.76   $239.75   $239.80  
  Purchase #5 $70.75   8.542%   $76.7935   $76.79   $76.80   $76.80  
  Purchase #6 $144.45   3.642%   $149.7109   $149.71   $149.70   $149.70  
  Purchase #7 $157.32   5.242%   $165.5667   $165.57   $165.55   $165.60  
  7 purchase totals = $986.34       $1,087.6493   $1,087.65   $1,087.65   $1,087.60