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 $56.59   9.114%   $61.7476   $61.75   $61.75   $61.70  
  Purchase #2 $86.81   12.364%   $97.5432   $97.54   $97.55   $97.50  
  Purchase #3 $159.55   10.350%   $176.0634   $176.06   $176.05   $176.10  
  Purchase #4 $16.51   8.810%   $17.9645   $17.96   $17.95   $18.00  
  Purchase #5 $183.99   4.401%   $192.0874   $192.09   $192.10   $192.10  
  Purchase #6 $194.91   4.678%   $204.0279   $204.03   $204.05   $204.00  
  Purchase #7 $226.32   6.138%   $240.2115   $240.21   $240.20   $240.20  
  7 purchase totals = $924.68       $989.6455   $989.64   $989.65   $989.60