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	$245.57	12.113%	$275.3159	$275.32	$275.30	$275.30
Purchase #2	$218.75	9.180%	$238.8313	$238.83	$238.85	$238.80
Purchase #3	$53.32	13.251%	$60.3854	$60.39	$60.40	$60.40
Purchase #4	$169.90	5.807%	$179.7661	$179.77	$179.75	$179.80
Purchase #5	$126.77	3.682%	$131.4377	$131.44	$131.45	$131.40
Purchase #6	$168.91	6.641%	$180.1273	$180.13	$180.15	$180.10
Purchase #7	$223.70	3.738%	$232.0619	$232.06	$232.05	$232.10
7 purchase totals =	$1,206.92		$1,297.9256	$1,297.94	$1,297.95	$1,297.90