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	$79.41	4.779%	$83.205	$83.21	$83.20	$83.20
Purchase #2	$102.28	8.263%	$110.7314	$110.73	$110.75	$110.70
Purchase #3	$39.32	3.410%	$40.6608	$40.66	$40.65	$40.70
Purchase #4	$79.77	13.343%	$90.4137	$90.41	$90.40	$90.40
Purchase #5	$71.70	3.128%	$73.9428	$73.94	$73.95	$73.90
Purchase #6	$145.33	11.765%	$162.4281	$162.43	$162.45	$162.40
Purchase #7	$39.44	7.765%	$42.5025	$42.50	$42.50	$42.50
7 purchase totals =	$557.25		$603.8843	$603.88	$603.90	$603.80