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 $237.27   11.187%   $263.8134   $263.81   $263.80   $263.80  
  Purchase #2 $158.78   11.282%   $176.6936   $176.69   $176.70   $176.70  
  Purchase #3 $13.95   9.128%   $15.2234   $15.22   $15.20   $15.20  
  Purchase #4 $201.73   8.459%   $218.7943   $218.79   $218.80   $218.80  
  Purchase #5 $68.33   8.296%   $73.9987   $74.00   $74.00   $74.00  
  Purchase #6 $196.34   5.163%   $206.477   $206.48   $206.50   $206.50  
  Purchase #7 $76.35   7.155%   $81.8128   $81.81   $81.80   $81.80  
  7 purchase totals = $952.75       $1,036.8132   $1,036.80   $1,036.80   $1,036.80