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 $48.33   10.802%   $53.5506   $53.55   $53.55   $53.60  
  Purchase #2 $61.62   10.868%   $68.3169   $68.32   $68.30   $68.30  
  Purchase #3 $60.47   10.515%   $66.8284   $66.83   $66.85   $66.80  
  Purchase #4 $136.79   11.668%   $152.7507   $152.75   $152.75   $152.80  
  Purchase #5 $215.43   8.871%   $234.5408   $234.54   $234.55   $234.50  
  Purchase #6 $182.32   4.318%   $190.1926   $190.19   $190.20   $190.20  
  Purchase #7 $74.69   4.196%   $77.824   $77.82   $77.80   $77.80  
  7 purchase totals = $779.65       $844.0040   $844.00   $844.00   $844.00