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	$73.68	4.136%	$76.7274	$76.73	$76.75	$76.70
Purchase #2	$79.77	7.223%	$85.5318	$85.53	$85.55	$85.50
Purchase #3	$227.49	10.209%	$250.7145	$250.71	$250.70	$250.70
Purchase #4	$84.26	6.129%	$89.4243	$89.42	$89.40	$89.40
Purchase #5	$118.31	13.391%	$134.1529	$134.15	$134.15	$134.20
Purchase #6	$29.54	9.566%	$32.3658	$32.37	$32.35	$32.40
Purchase #7	$132.40	7.267%	$142.0215	$142.02	$142.00	$142.00
7 purchase totals =	$745.45		$810.9382	$810.93	$810.90	$810.90