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 $42.64   8.706%   $46.3522   $46.35   $46.35   $46.40  
  Purchase #2 $247.25   11.646%   $276.0447   $276.04   $276.05   $276.00  
  Purchase #3 $10.98   7.110%   $11.7607   $11.76   $11.75   $11.80  
  Purchase #4 $60.68   4.498%   $63.4094   $63.41   $63.40   $63.40  
  Purchase #5 $32.41   7.550%   $34.857   $34.86   $34.85   $34.90  
  Purchase #6 $126.60   8.388%   $137.2192   $137.22   $137.20   $137.20  
  Purchase #7 $34.92   6.166%   $37.0732   $37.07   $37.05   $37.10  
  7 purchase totals = $555.48       $606.7164   $606.71   $606.65   $606.80