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 $164.76   13.243%   $186.5792   $186.58   $186.60   $186.60  
  Purchase #2 $131.74   4.636%   $137.8475   $137.85   $137.85   $137.80  
  Purchase #3 $213.94   12.655%   $241.0141   $241.01   $241.00   $241.00  
  Purchase #4 $212.68   10.734%   $235.5091   $235.51   $235.50   $235.50  
  Purchase #5 $21.51   6.848%   $22.983   $22.98   $23.00   $23.00  
  Purchase #6 $117.62   7.422%   $126.3498   $126.35   $126.35   $126.30  
  Purchase #7 $43.96   4.139%   $45.7795   $45.78   $45.80   $45.80  
  7 purchase totals = $906.21       $996.0622   $996.06   $996.10   $996.00