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 $178.98   7.177%   $191.8254   $191.83   $191.85   $191.80  
  Purchase #2 $102.49   7.652%   $110.3325   $110.33   $110.35   $110.30  
  Purchase #3 $190.26   4.774%   $199.343   $199.34   $199.35   $199.30  
  Purchase #4 $240.57   10.874%   $266.7296   $266.73   $266.75   $266.70  
  Purchase #5 $183.90   4.556%   $192.2785   $192.28   $192.30   $192.30  
  Purchase #6 $17.66   8.246%   $19.1162   $19.12   $19.10   $19.10  
  Purchase #7 $42.62   9.542%   $46.6868   $46.69   $46.70   $46.70  
  7 purchase totals = $956.48       $1,026.3120   $1,026.32   $1,026.40   $1,026.20