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 $188.51   11.239%   $209.6966   $209.70   $209.70   $209.70  
  Purchase #2 $55.93   12.109%   $62.7026   $62.70   $62.70   $62.70  
  Purchase #3 $121.77   4.467%   $127.2095   $127.21   $127.20   $127.20  
  Purchase #4 $198.66   12.146%   $222.7892   $222.79   $222.80   $222.80  
  Purchase #5 $164.26   7.135%   $175.98   $175.98   $176.00   $176.00  
  Purchase #6 $155.83   3.536%   $161.3401   $161.34   $161.35   $161.30  
  Purchase #7 $23.82   13.196%   $26.9633   $26.96   $26.95   $27.00  
  7 purchase totals = $908.78       $986.6813   $986.68   $986.70   $986.70