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	$110.27	12.355%	$123.8939	$123.89	$123.90	$123.90
Purchase #2	$165.40	13.352%	$187.4842	$187.48	$187.50	$187.50
Purchase #3	$68.41	7.106%	$73.2712	$73.27	$73.25	$73.30
Purchase #4	$95.81	8.583%	$104.0334	$104.03	$104.05	$104.00
Purchase #5	$162.51	12.719%	$183.1796	$183.18	$183.20	$183.20
Purchase #6	$238.48	13.186%	$269.926	$269.93	$269.95	$269.90
Purchase #7	$233.90	9.853%	$256.9462	$256.95	$256.95	$256.90
7 purchase totals =	$1,074.78		$1,198.7345	$1,198.73	$1,198.80	$1,198.70