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 $210.72   13.677%   $239.5402   $239.54   $239.55   $239.50  
  Purchase #2 $63.97   9.483%   $70.0363   $70.04   $70.05   $70.00  
  Purchase #3 $240.83   11.390%   $268.2605   $268.26   $268.25   $268.30  
  Purchase #4 $33.88   12.411%   $38.0848   $38.08   $38.10   $38.10  
  Purchase #5 $186.53   7.764%   $201.0122   $201.01   $201.00   $201.00  
  Purchase #6 $89.69   7.621%   $96.5253   $96.53   $96.55   $96.50  
  Purchase #7 $33.85   12.668%   $38.1381   $38.14   $38.15   $38.10  
  7 purchase totals = $859.47       $951.5974   $951.60   $951.65   $951.50