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 $86.39   11.144%   $96.0173   $96.02   $96.00   $96.00  
  Purchase #2 $47.51   10.294%   $52.4007   $52.40   $52.40   $52.40  
  Purchase #3 $188.73   10.102%   $207.7955   $207.80   $207.80   $207.80  
  Purchase #4 $154.63   9.734%   $169.6817   $169.68   $169.70   $169.70  
  Purchase #5 $35.75   6.529%   $38.0841   $38.08   $38.10   $38.10  
  Purchase #6 $171.51   6.635%   $182.8897   $182.89   $182.90   $182.90  
  Purchase #7 $204.48   5.572%   $215.8736   $215.87   $215.85   $215.90  
  7 purchase totals = $889.00       $962.7426   $962.74   $962.75   $962.80