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 $134.52   12.622%   $151.4991   $151.50   $151.50   $151.50  
  Purchase #2 $65.73   13.792%   $74.7955   $74.80   $74.80   $74.80  
  Purchase #3 $11.79   6.314%   $12.5344   $12.53   $12.55   $12.50  
  Purchase #4 $248.87   10.377%   $274.6952   $274.70   $274.70   $274.70  
  Purchase #5 $73.86   5.463%   $77.895   $77.90   $77.90   $77.90  
  Purchase #6 $94.68   10.337%   $104.4671   $104.47   $104.45   $104.50  
  Purchase #7 $192.78   8.414%   $209.0005   $209.00   $209.00   $209.00  
  7 purchase totals = $822.23       $904.8868   $904.90   $904.90   $904.90