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 $163.82   11.685%   $182.9624   $182.96   $182.95   $183.00  
  Purchase #2 $129.45   4.643%   $135.4604   $135.46   $135.45   $135.50  
  Purchase #3 $105.27   5.464%   $111.022   $111.02   $111.00   $111.00  
  Purchase #4 $177.56   6.227%   $188.6167   $188.62   $188.60   $188.60  
  Purchase #5 $14.80   13.297%   $16.768   $16.77   $16.75   $16.80  
  Purchase #6 $139.64   11.369%   $155.5157   $155.52   $155.50   $155.50  
  Purchase #7 $38.44   3.357%   $39.7304   $39.73   $39.75   $39.70  
  7 purchase totals = $768.98       $830.0756   $830.08   $830.00   $830.10