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	$40.31	4.428%	$42.0949	$42.09	$42.10	$42.10
Purchase #2	$56.48	4.234%	$58.8714	$58.87	$58.85	$58.90
Purchase #3	$57.96	8.571%	$62.9278	$62.93	$62.95	$62.90
Purchase #4	$158.91	4.628%	$166.2644	$166.26	$166.25	$166.30
Purchase #5	$18.66	9.159%	$20.3691	$20.37	$20.35	$20.40
Purchase #6	$71.51	12.312%	$80.3143	$80.31	$80.30	$80.30
Purchase #7	$148.43	5.396%	$156.4393	$156.44	$156.45	$156.40
7 purchase totals =	$552.26		$587.2812	$587.27	$587.25	$587.30