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 $61.46   5.776%   $65.0099   $65.01   $65.00   $65.00  
  Purchase #2 $196.88   8.759%   $214.1247   $214.12   $214.10   $214.10  
  Purchase #3 $101.79   10.190%   $112.1624   $112.16   $112.15   $112.20  
  Purchase #4 $245.84   10.401%   $271.4098   $271.41   $271.40   $271.40  
  Purchase #5 $86.60   6.495%   $92.2247   $92.22   $92.20   $92.20  
  Purchase #6 $188.63   6.645%   $201.1645   $201.16   $201.15   $201.20  
  Purchase #7 $29.68   5.705%   $31.3732   $31.37   $31.35   $31.40  
  7 purchase totals = $910.88       $987.4692   $987.45   $987.35   $987.50