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 $48.99   8.272%   $53.0425   $53.04   $53.05   $53.00  
  Purchase #2 $201.88   9.194%   $220.4408   $220.44   $220.45   $220.40  
  Purchase #3 $24.44   11.563%   $27.266   $27.27   $27.25   $27.30  
  Purchase #4 $226.46   3.587%   $234.5831   $234.58   $234.60   $234.60  
  Purchase #5 $187.58   11.741%   $209.6038   $209.60   $209.60   $209.60  
  Purchase #6 $137.94   10.215%   $152.0306   $152.03   $152.05   $152.00  
  Purchase #7 $222.39   7.865%   $239.881   $239.88   $239.90   $239.90  
  7 purchase totals = $1,049.68       $1,136.8478   $1,136.84   $1,136.90   $1,136.80