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	$238.71	10.786%	$264.4573	$264.46	$264.45	$264.50
Purchase #2	$22.77	11.541%	$25.3979	$25.40	$25.40	$25.40
Purchase #3	$48.60	12.382%	$54.6177	$54.62	$54.60	$54.60
Purchase #4	$86.85	5.780%	$91.8699	$91.87	$91.85	$91.90
Purchase #5	$174.74	10.481%	$193.0545	$193.05	$193.05	$193.10
Purchase #6	$86.60	3.507%	$89.6371	$89.64	$89.65	$89.60
Purchase #7	$42.86	11.254%	$47.6835	$47.68	$47.70	$47.70
7 purchase totals =	$701.13		$766.7179	$766.72	$766.70	$766.80