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	$229.63	6.302%	$244.1013	$244.10	$244.10	$244.10
Purchase #2	$243.46	4.257%	$253.8241	$253.82	$253.80	$253.80
Purchase #3	$165.53	12.320%	$185.9233	$185.92	$185.90	$185.90
Purchase #4	$110.64	3.174%	$114.1517	$114.15	$114.15	$114.20
Purchase #5	$149.90	12.665%	$168.8848	$168.88	$168.90	$168.90
Purchase #6	$27.44	12.714%	$30.9287	$30.93	$30.95	$30.90
Purchase #7	$6.90	5.764%	$7.2977	$7.30	$7.30	$7.30
7 purchase totals =	$933.50		$1,005.1116	$1,005.10	$1,005.10	$1,005.10