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 $90.94   6.307%   $96.6756   $96.68   $96.70   $96.70  
  Purchase #2 $141.39   8.868%   $153.9285   $153.93   $153.95   $153.90  
  Purchase #3 $50.53   12.124%   $56.6563   $56.66   $56.65   $56.70  
  Purchase #4 $177.49   9.870%   $195.0083   $195.01   $195.00   $195.00  
  Purchase #5 $186.47   8.453%   $202.2323   $202.23   $202.25   $202.20  
  Purchase #6 $193.28   13.446%   $219.2684   $219.27   $219.25   $219.30  
  Purchase #7 $188.77   10.152%   $207.9339   $207.93   $207.95   $207.90  
  7 purchase totals = $1,028.87       $1,131.7033   $1,131.71   $1,131.75   $1,131.70