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 $216.96   11.827%   $242.6199   $242.62   $242.60   $242.60  
  Purchase #2 $176.87   9.606%   $193.8601   $193.86   $193.85   $193.90  
  Purchase #3 $238.30   10.616%   $263.5979   $263.60   $263.60   $263.60  
  Purchase #4 $70.26   12.240%   $78.8598   $78.86   $78.85   $78.90  
  Purchase #5 $16.71   4.798%   $17.5117   $17.51   $17.50   $17.50  
  Purchase #6 $29.37   5.574%   $31.0071   $31.01   $31.00   $31.00  
  Purchase #7 $223.46   9.803%   $245.3658   $245.37   $245.35   $245.40  
  7 purchase totals = $971.93       $1,072.8223   $1,072.83   $1,072.75   $1,072.90