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 $202.42   10.810%   $224.3016   $224.30   $224.30   $224.30  
  Purchase #2 $167.85   8.826%   $182.6644   $182.66   $182.65   $182.70  
  Purchase #3 $127.83   12.211%   $143.4393   $143.44   $143.45   $143.40  
  Purchase #4 $214.76   8.845%   $233.7555   $233.76   $233.75   $233.80  
  Purchase #5 $50.80   13.103%   $57.4563   $57.46   $57.45   $57.50  
  Purchase #6 $145.67   10.746%   $161.3237   $161.32   $161.30   $161.30  
  Purchase #7 $38.85   8.387%   $42.1083   $42.11   $42.10   $42.10  
  7 purchase totals = $948.18       $1,045.0491   $1,045.05   $1,045.00   $1,045.10