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 $160.80   13.564%   $182.6109   $182.61   $182.60   $182.60  
  Purchase #2 $95.37   7.338%   $102.3683   $102.37   $102.35   $102.40  
  Purchase #3 $113.39   12.158%   $127.176   $127.18   $127.20   $127.20  
  Purchase #4 $65.63   11.501%   $73.1781   $73.18   $73.20   $73.20  
  Purchase #5 $121.46   8.577%   $131.8776   $131.88   $131.90   $131.90  
  Purchase #6 $165.34   5.405%   $174.2766   $174.28   $174.30   $174.30  
  Purchase #7 $136.68   8.779%   $148.6791   $148.68   $148.70   $148.70  
  7 purchase totals = $858.67       $940.1666   $940.18   $940.25   $940.30