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 $118.53   4.516%   $123.8828   $123.88   $123.90   $123.90  
  Purchase #2 $165.70   10.818%   $183.6254   $183.63   $183.65   $183.60  
  Purchase #3 $230.27   11.358%   $256.4241   $256.42   $256.40   $256.40  
  Purchase #4 $116.29   4.578%   $121.6138   $121.61   $121.60   $121.60  
  Purchase #5 $145.44   12.357%   $163.412   $163.41   $163.40   $163.40  
  Purchase #6 $246.25   5.567%   $259.9587   $259.96   $259.95   $260.00  
  Purchase #7 $157.27   13.854%   $179.0582   $179.06   $179.05   $179.10  
  7 purchase totals = $1,179.75       $1,287.9750   $1,287.97   $1,287.95   $1,288.00