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 $70.68   4.365%   $73.7652   $73.77   $73.75   $73.80  
  Purchase #2 $171.92   12.642%   $193.6541   $193.65   $193.65   $193.70  
  Purchase #3 $92.66   5.238%   $97.5135   $97.51   $97.50   $97.50  
  Purchase #4 $113.71   8.716%   $123.621   $123.62   $123.60   $123.60  
  Purchase #5 $99.25   5.844%   $105.0502   $105.05   $105.05   $105.10  
  Purchase #6 $54.58   3.730%   $56.6158   $56.62   $56.60   $56.60  
  Purchase #7 $12.72   6.330%   $13.5252   $13.53   $13.55   $13.50  
  7 purchase totals = $615.52       $663.7450   $663.75   $663.70   $663.80