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 $61.35   6.873%   $65.5666   $65.57   $65.55   $65.60  
  Purchase #2 $121.73   3.554%   $126.0563   $126.06   $126.05   $126.10  
  Purchase #3 $27.35   9.169%   $29.8577   $29.86   $29.85   $29.90  
  Purchase #4 $250.36   6.136%   $265.7221   $265.72   $265.70   $265.70  
  Purchase #5 $60.57   13.338%   $68.6488   $68.65   $68.65   $68.60  
  Purchase #6 $67.50   10.336%   $74.4768   $74.48   $74.50   $74.50  
  Purchase #7 $85.26   10.153%   $93.9164   $93.92   $93.90   $93.90  
  7 purchase totals = $674.12       $724.2447   $724.26   $724.20   $724.30