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 $60.76   13.207%   $68.7846   $68.78   $68.80   $68.80  
  Purchase #2 $114.54   10.284%   $126.3193   $126.32   $126.30   $126.30  
  Purchase #3 $198.83   13.529%   $225.7297   $225.73   $225.75   $225.70  
  Purchase #4 $199.60   12.492%   $224.534   $224.53   $224.55   $224.50  
  Purchase #5 $147.73   13.787%   $168.0975   $168.10   $168.10   $168.10  
  Purchase #6 $101.87   3.649%   $105.5872   $105.59   $105.60   $105.60  
  Purchase #7 $33.72   5.822%   $35.6832   $35.68   $35.70   $35.70  
  7 purchase totals = $857.05       $954.7355   $954.73   $954.80   $954.70