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 $85.94   10.726%   $95.1579   $95.16   $95.15   $95.20  
  Purchase #2 $250.92   3.208%   $258.9695   $258.97   $258.95   $259.00  
  Purchase #3 $22.80   13.869%   $25.9621   $25.96   $25.95   $26.00  
  Purchase #4 $127.28   13.208%   $144.0911   $144.09   $144.10   $144.10  
  Purchase #5 $188.57   7.620%   $202.939   $202.94   $202.95   $202.90  
  Purchase #6 $39.81   7.519%   $42.8033   $42.80   $42.80   $42.80  
  Purchase #7 $54.40   8.651%   $59.1061   $59.11   $59.10   $59.10  
  7 purchase totals = $769.72       $829.0290   $829.03   $829.00   $829.10