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   9.543%   $269.7606   $269.76   $269.75   $269.80  
  Purchase #2 $41.47   4.194%   $43.2093   $43.21   $43.20   $43.20  
  Purchase #3 $227.53   6.669%   $242.704   $242.70   $242.70   $242.70  
  Purchase #4 $240.47   4.313%   $250.8415   $250.84   $250.85   $250.80  
  Purchase #5 $57.96   10.704%   $64.164   $64.16   $64.15   $64.20  
  Purchase #6 $209.69   6.819%   $223.9888   $223.99   $224.00   $224.00  
  Purchase #7 $147.59   10.622%   $163.267   $163.27   $163.25   $163.30  
  7 purchase totals = $1,170.97       $1,257.9352   $1,257.93   $1,257.90   $1,258.00