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 $93.55   10.456%   $103.3316   $103.33   $103.35   $103.30  
  Purchase #2 $61.64   7.168%   $66.0584   $66.06   $66.05   $66.10  
  Purchase #3 $198.26   11.486%   $221.0321   $221.03   $221.05   $221.00  
  Purchase #4 $239.42   6.261%   $254.4101   $254.41   $254.40   $254.40  
  Purchase #5 $188.42   11.696%   $210.4576   $210.46   $210.45   $210.50  
  Purchase #6 $233.43   8.375%   $252.9798   $252.98   $253.00   $253.00  
  Purchase #7 $80.43   7.573%   $86.521   $86.52   $86.50   $86.50  
  7 purchase totals = $1,095.15       $1,194.7906   $1,194.79   $1,194.80   $1,194.80