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 $179.69   8.518%   $194.996   $195.00   $195.00   $195.00  
  Purchase #2 $20.91   10.113%   $23.0246   $23.02   $23.00   $23.00  
  Purchase #3 $209.28   10.710%   $231.6939   $231.69   $231.70   $231.70  
  Purchase #4 $38.62   11.319%   $42.9914   $42.99   $43.00   $43.00  
  Purchase #5 $144.83   5.500%   $152.7957   $152.80   $152.80   $152.80  
  Purchase #6 $54.35   6.151%   $57.6931   $57.69   $57.70   $57.70  
  Purchase #7 $142.94   8.622%   $155.2643   $155.26   $155.25   $155.30  
  7 purchase totals = $790.62       $858.4590   $858.45   $858.45   $858.50