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	$33.72	13.399%	$38.2381	$38.24	$38.25	$38.20
Purchase #2	$86.85	5.486%	$91.6146	$91.61	$91.60	$91.60
Purchase #3	$142.69	13.231%	$161.5693	$161.57	$161.55	$161.60
Purchase #4	$172.46	11.264%	$191.8859	$191.89	$191.90	$191.90
Purchase #5	$56.80	13.290%	$64.3487	$64.35	$64.35	$64.30
Purchase #6	$133.38	13.391%	$151.2409	$151.24	$151.25	$151.20
Purchase #7	$14.70	8.238%	$15.911	$15.91	$15.90	$15.90
7 purchase totals =	$640.60		$714.8085	$714.81	$714.80	$714.70