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 $153.75   9.325%   $168.0872   $168.09   $168.10   $168.10  
  Purchase #2 $236.80   9.720%   $259.817   $259.82   $259.80   $259.80  
  Purchase #3 $244.55   8.135%   $264.4441   $264.44   $264.45   $264.40  
  Purchase #4 $243.77   7.548%   $262.1698   $262.17   $262.15   $262.20  
  Purchase #5 $67.59   8.417%   $73.2791   $73.28   $73.30   $73.30  
  Purchase #6 $108.67   6.412%   $115.6379   $115.64   $115.65   $115.60  
  Purchase #7 $163.59   3.540%   $169.3811   $169.38   $169.40   $169.40  
  7 purchase totals = $1,218.72       $1,312.8162   $1,312.82   $1,312.85   $1,312.80