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 $46.54   12.681%   $52.4417   $52.44   $52.45   $52.40  
  Purchase #2 $132.28   6.338%   $140.6639   $140.66   $140.65   $140.70  
  Purchase #3 $219.95   13.167%   $248.9108   $248.91   $248.90   $248.90  
  Purchase #4 $106.54   8.611%   $115.7142   $115.71   $115.70   $115.70  
  Purchase #5 $99.96   11.520%   $111.4754   $111.48   $111.50   $111.50  
  Purchase #6 $187.57   3.834%   $194.7614   $194.76   $194.75   $194.80  
  Purchase #7 $73.42   3.824%   $76.2276   $76.23   $76.25   $76.20  
  7 purchase totals = $866.26       $940.1950   $940.19   $940.20   $940.20