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 $183.64   13.264%   $207.998   $208.00   $208.00   $208.00  
  Purchase #2 $124.79   3.191%   $128.772   $128.77   $128.75   $128.80  
  Purchase #3 $33.87   12.855%   $38.224   $38.22   $38.20   $38.20  
  Purchase #4 $135.34   4.680%   $141.6739   $141.67   $141.65   $141.70  
  Purchase #5 $210.96   11.183%   $234.5517   $234.55   $234.55   $234.60  
  Purchase #6 $113.98   7.784%   $122.8522   $122.85   $122.85   $122.90  
  Purchase #7 $90.25   7.408%   $96.9357   $96.94   $96.95   $96.90  
  7 purchase totals = $892.83       $971.0075   $971.00   $970.95   $971.10