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 $69.69   11.582%   $77.7615   $77.76   $77.75   $77.80  
  Purchase #2 $165.58   4.282%   $172.6701   $172.67   $172.65   $172.70  
  Purchase #3 $223.80   11.670%   $249.9175   $249.92   $249.90   $249.90  
  Purchase #4 $248.45   12.489%   $279.4789   $279.48   $279.50   $279.50  
  Purchase #5 $222.95   11.543%   $248.6851   $248.69   $248.70   $248.70  
  Purchase #6 $223.53   10.446%   $246.8799   $246.88   $246.90   $246.90  
  Purchase #7 $169.98   12.455%   $191.151   $191.15   $191.15   $191.20  
  7 purchase totals = $1,323.98       $1,466.5440   $1,466.55   $1,466.55   $1,466.70