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 $138.68   5.393%   $146.159   $146.16   $146.15   $146.20  
  Purchase #2 $161.56   8.271%   $174.9226   $174.92   $174.90   $174.90  
  Purchase #3 $183.43   12.124%   $205.6691   $205.67   $205.65   $205.70  
  Purchase #4 $157.65   5.761%   $166.7322   $166.73   $166.75   $166.70  
  Purchase #5 $34.27   6.509%   $36.5006   $36.50   $36.50   $36.50  
  Purchase #6 $231.98   8.478%   $251.6473   $251.65   $251.65   $251.60  
  Purchase #7 $76.57   6.397%   $81.4682   $81.47   $81.45   $81.50  
  7 purchase totals = $984.14       $1,063.0990   $1,063.10   $1,063.05   $1,063.10