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	$237.37	12.120%	$266.1392	$266.14	$266.15	$266.10
Purchase #2	$53.84	7.343%	$57.7935	$57.79	$57.80	$57.80
Purchase #3	$185.93	8.815%	$202.3197	$202.32	$202.30	$202.30
Purchase #4	$95.50	8.434%	$103.5545	$103.55	$103.55	$103.60
Purchase #5	$244.50	7.608%	$263.1016	$263.10	$263.10	$263.10
Purchase #6	$59.48	8.408%	$64.4811	$64.48	$64.50	$64.50
Purchase #7	$97.40	6.262%	$103.4992	$103.50	$103.50	$103.50
7 purchase totals =	$974.02		$1,060.8888	$1,060.88	$1,060.90	$1,060.90