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 $86.29   11.412%   $96.1374   $96.14   $96.15   $96.10  
  Purchase #2 $56.88   4.864%   $59.6466   $59.65   $59.65   $59.60  
  Purchase #3 $244.84   6.704%   $261.2541   $261.25   $261.25   $261.30  
  Purchase #4 $221.59   6.184%   $235.2931   $235.29   $235.30   $235.30  
  Purchase #5 $210.30   13.792%   $239.3046   $239.30   $239.30   $239.30  
  Purchase #6 $246.80   4.354%   $257.5457   $257.55   $257.55   $257.50  
  Purchase #7 $44.69   13.496%   $50.7214   $50.72   $50.70   $50.70  
  7 purchase totals = $1,111.39       $1,199.9029   $1,199.90   $1,199.90   $1,199.80