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 $148.76   13.778%   $169.2562   $169.26   $169.25   $169.30  
  Purchase #2 $128.36   9.706%   $140.8186   $140.82   $140.80   $140.80  
  Purchase #3 $167.46   12.644%   $188.6336   $188.63   $188.65   $188.60  
  Purchase #4 $82.52   12.249%   $92.6279   $92.63   $92.65   $92.60  
  Purchase #5 $250.49   5.421%   $264.0691   $264.07   $264.05   $264.10  
  Purchase #6 $68.71   3.255%   $70.9465   $70.95   $70.95   $70.90  
  Purchase #7 $157.26   7.304%   $168.7463   $168.75   $168.75   $168.70  
  7 purchase totals = $1,003.56       $1,095.0982   $1,095.11   $1,095.10   $1,095.00