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 $226.46   6.749%   $241.7438   $241.74   $241.75   $241.70  
  Purchase #2 $150.89   12.127%   $169.1884   $169.19   $169.20   $169.20  
  Purchase #3 $159.83   8.464%   $173.358   $173.36   $173.35   $173.40  
  Purchase #4 $222.69   3.531%   $230.5532   $230.55   $230.55   $230.60  
  Purchase #5 $158.74   8.317%   $171.9424   $171.94   $171.95   $171.90  
  Purchase #6 $18.56   6.718%   $19.8069   $19.81   $19.80   $19.80  
  Purchase #7 $158.58   4.832%   $166.2426   $166.24   $166.25   $166.20  
  7 purchase totals = $1,095.75       $1,172.8353   $1,172.83   $1,172.85   $1,172.80