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	$32.86	3.214%	$33.9161	$33.92	$33.90	$33.90
Purchase #2	$202.75	9.432%	$221.8734	$221.87	$221.85	$221.90
Purchase #3	$55.34	3.397%	$57.2199	$57.22	$57.20	$57.20
Purchase #4	$20.29	4.205%	$21.1432	$21.14	$21.15	$21.10
Purchase #5	$178.97	6.326%	$190.2916	$190.29	$190.30	$190.30
Purchase #6	$62.58	11.399%	$69.7135	$69.71	$69.70	$69.70
Purchase #7	$65.60	12.138%	$73.5625	$73.56	$73.55	$73.60
7 purchase totals =	$618.39		$667.7202	$667.71	$667.65	$667.70