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	$217.30	9.761%	$238.5107	$238.51	$238.50	$238.50
Purchase #2	$161.88	3.538%	$167.6073	$167.61	$167.60	$167.60
Purchase #3	$123.83	11.132%	$137.6148	$137.61	$137.60	$137.60
Purchase #4	$227.70	12.763%	$256.7614	$256.76	$256.75	$256.80
Purchase #5	$131.82	7.228%	$141.3479	$141.35	$141.35	$141.30
Purchase #6	$204.31	5.764%	$216.0864	$216.09	$216.10	$216.10
Purchase #7	$245.88	5.666%	$259.8116	$259.81	$259.80	$259.80
7 purchase totals =	$1,312.72		$1,417.7401	$1,417.74	$1,417.70	$1,417.70