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 $208.41   10.711%   $230.7328   $230.73   $230.75   $230.70  
  Purchase #2 $95.97   7.501%   $103.1687   $103.17   $103.15   $103.20  
  Purchase #3 $117.34   13.612%   $133.3123   $133.31   $133.30   $133.30  
  Purchase #4 $68.47   8.455%   $74.2591   $74.26   $74.25   $74.30  
  Purchase #5 $182.28   11.608%   $203.4391   $203.44   $203.45   $203.40  
  Purchase #6 $67.85   13.461%   $76.9833   $76.98   $77.00   $77.00  
  Purchase #7 $157.64   5.366%   $166.099   $166.10   $166.10   $166.10  
  7 purchase totals = $897.96       $987.9943   $987.99   $988.00   $988.00