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 $246.26   9.626%   $269.965   $269.97   $269.95   $270.00  
  Purchase #2 $101.93   9.626%   $111.7418   $111.74   $111.75   $111.70  
  Purchase #3 $231.55   11.418%   $257.9884   $257.99   $258.00   $258.00  
  Purchase #4 $165.43   11.110%   $183.8093   $183.81   $183.80   $183.80  
  Purchase #5 $21.94   6.108%   $23.2801   $23.28   $23.30   $23.30  
  Purchase #6 $108.53   9.271%   $118.5918   $118.59   $118.60   $118.60  
  Purchase #7 $215.98   5.537%   $227.9388   $227.94   $227.95   $227.90  
  7 purchase totals = $1,091.62       $1,193.3152   $1,193.32   $1,193.35   $1,193.30