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 $142.59   12.262%   $160.0744   $160.07   $160.05   $160.10  
  Purchase #2 $165.72   8.430%   $179.6902   $179.69   $179.70   $179.70  
  Purchase #3 $246.91   8.855%   $268.7739   $268.77   $268.75   $268.80  
  Purchase #4 $68.42   4.447%   $71.4626   $71.46   $71.45   $71.50  
  Purchase #5 $6.61   6.561%   $7.0437   $7.04   $7.05   $7.00  
  Purchase #6 $161.65   4.572%   $169.0406   $169.04   $169.05   $169.00  
  Purchase #7 $151.81   10.724%   $168.0901   $168.09   $168.10   $168.10  
  7 purchase totals = $943.71       $1,024.1755   $1,024.16   $1,024.15   $1,024.20