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 $134.60   10.724%   $149.0345   $149.03   $149.05   $149.00  
  Purchase #2 $176.40   11.145%   $196.0598   $196.06   $196.05   $196.10  
  Purchase #3 $205.42   8.589%   $223.0635   $223.06   $223.05   $223.10  
  Purchase #4 $241.82   11.312%   $269.1747   $269.17   $269.15   $269.20  
  Purchase #5 $66.91   8.720%   $72.7446   $72.74   $72.75   $72.70  
  Purchase #6 $190.47   9.783%   $209.1037   $209.10   $209.10   $209.10  
  Purchase #7 $228.55   7.658%   $246.0524   $246.05   $246.05   $246.10  
  7 purchase totals = $1,244.17       $1,365.2332   $1,365.21   $1,365.20   $1,365.30