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 $83.86   3.322%   $86.6458   $86.65   $86.65   $86.60  
  Purchase #2 $246.40   10.764%   $272.9225   $272.92   $272.90   $272.90  
  Purchase #3 $83.36   12.727%   $93.9692   $93.97   $93.95   $94.00  
  Purchase #4 $168.51   11.834%   $188.4515   $188.45   $188.45   $188.50  
  Purchase #5 $134.96   13.373%   $153.0082   $153.01   $153.00   $153.00  
  Purchase #6 $181.77   12.305%   $204.1368   $204.14   $204.15   $204.10  
  Purchase #7 $226.76   5.460%   $239.1411   $239.14   $239.15   $239.10  
  7 purchase totals = $1,125.62       $1,238.2751   $1,238.28   $1,238.25   $1,238.20