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	$50.77	11.416%	$56.5659	$56.57	$56.55	$56.60
Purchase #2	$215.90	10.344%	$238.2327	$238.23	$238.25	$238.20
Purchase #3	$247.30	6.257%	$262.7736	$262.77	$262.75	$262.80
Purchase #4	$228.36	11.584%	$254.8132	$254.81	$254.80	$254.80
Purchase #5	$89.41	12.516%	$100.6006	$100.60	$100.60	$100.60
Purchase #6	$168.42	13.845%	$191.7377	$191.74	$191.75	$191.70
Purchase #7	$179.65	9.445%	$196.6179	$196.62	$196.60	$196.60
7 purchase totals =	$1,179.81		$1,301.3416	$1,301.34	$1,301.30	$1,301.30