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 $27.48   7.789%   $29.6204   $29.62   $29.60   $29.60  
  Purchase #2 $231.32   6.219%   $245.7058   $245.71   $245.70   $245.70  
  Purchase #3 $149.71   3.254%   $154.5816   $154.58   $154.60   $154.60  
  Purchase #4 $118.66   4.783%   $124.3355   $124.34   $124.35   $124.30  
  Purchase #5 $249.31   6.719%   $266.0611   $266.06   $266.05   $266.10  
  Purchase #6 $66.82   11.532%   $74.5257   $74.53   $74.55   $74.50  
  Purchase #7 $144.79   11.673%   $161.6913   $161.69   $161.70   $161.70  
  7 purchase totals = $988.09       $1,056.5214   $1,056.53   $1,056.55   $1,056.50