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 $65.92   5.466%   $69.5232   $69.52   $69.50   $69.50  
  Purchase #2 $225.75   8.806%   $245.6295   $245.63   $245.65   $245.60  
  Purchase #3 $63.44   10.192%   $69.9058   $69.91   $69.90   $69.90  
  Purchase #4 $244.70   8.666%   $265.9057   $265.91   $265.90   $265.90  
  Purchase #5 $64.28   12.519%   $72.3272   $72.33   $72.35   $72.30  
  Purchase #6 $86.36   7.566%   $92.894   $92.89   $92.90   $92.90  
  Purchase #7 $192.43   11.381%   $214.3305   $214.33   $214.35   $214.30  
  7 purchase totals = $942.88       $1,030.5159   $1,030.52   $1,030.55   $1,030.40