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 $46.98   5.698%   $49.6569   $49.66   $49.65   $49.70  
  Purchase #2 $85.94   13.588%   $97.6175   $97.62   $97.60   $97.60  
  Purchase #3 $180.71   7.190%   $193.703   $193.70   $193.70   $193.70  
  Purchase #4 $240.55   7.699%   $259.0699   $259.07   $259.05   $259.10  
  Purchase #5 $207.87   3.388%   $214.9126   $214.91   $214.90   $214.90  
  Purchase #6 $196.29   8.424%   $212.8255   $212.83   $212.85   $212.80  
  Purchase #7 $22.70   10.784%   $25.148   $25.15   $25.15   $25.10  
  7 purchase totals = $981.04       $1,052.9334   $1,052.94   $1,052.90   $1,052.90