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 $46.99   7.640%   $50.58   $50.58   $50.60   $50.60  
  Purchase #2 $176.70   3.478%   $182.8456   $182.85   $182.85   $182.80  
  Purchase #3 $182.36   6.248%   $193.7539   $193.75   $193.75   $193.80  
  Purchase #4 $135.97   5.693%   $143.7108   $143.71   $143.70   $143.70  
  Purchase #5 $181.47   10.570%   $200.6514   $200.65   $200.65   $200.70  
  Purchase #6 $236.62   10.776%   $262.1182   $262.12   $262.10   $262.10  
  Purchase #7 $151.47   13.301%   $171.617   $171.62   $171.60   $171.60  
  7 purchase totals = $1,111.58       $1,205.2769   $1,205.28   $1,205.25   $1,205.30