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 $47.91   10.167%   $52.781   $52.78   $52.80   $52.80  
  Purchase #2 $93.71   4.549%   $97.9729   $97.97   $97.95   $98.00  
  Purchase #3 $114.92   13.501%   $130.4353   $130.44   $130.45   $130.40  
  Purchase #4 $233.61   8.501%   $253.4692   $253.47   $253.45   $253.50  
  Purchase #5 $165.36   7.280%   $177.3982   $177.40   $177.40   $177.40  
  Purchase #6 $217.33   3.774%   $225.532   $225.53   $225.55   $225.50  
  Purchase #7 $111.34   8.198%   $120.4677   $120.47   $120.45   $120.50  
  7 purchase totals = $984.18       $1,058.0563   $1,058.06   $1,058.05   $1,058.10