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	$247.85	10.257%	$273.272	$273.27	$273.25	$273.30
Purchase #2	$163.93	5.736%	$173.333	$173.33	$173.35	$173.30
Purchase #3	$172.74	8.138%	$186.7976	$186.80	$186.80	$186.80
Purchase #4	$69.57	3.405%	$71.9389	$71.94	$71.95	$71.90
Purchase #5	$166.58	13.804%	$189.5747	$189.57	$189.55	$189.60
Purchase #6	$244.52	10.787%	$270.8964	$270.90	$270.90	$270.90
Purchase #7	$49.53	13.798%	$56.3641	$56.36	$56.35	$56.40
7 purchase totals =	$1,114.72		$1,222.1767	$1,222.17	$1,222.15	$1,222.20