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	$114.27	5.661%	$120.7388	$120.74	$120.75	$120.70
Purchase #2	$233.46	11.291%	$259.82	$259.82	$259.80	$259.80
Purchase #3	$240.81	5.434%	$253.8956	$253.90	$253.90	$253.90
Purchase #4	$54.98	12.252%	$61.7161	$61.72	$61.70	$61.70
Purchase #5	$101.93	3.700%	$105.7014	$105.70	$105.70	$105.70
Purchase #6	$60.62	12.427%	$68.1532	$68.15	$68.15	$68.20
Purchase #7	$166.98	3.250%	$172.4069	$172.41	$172.40	$172.40
7 purchase totals =	$973.05		$1,042.4320	$1,042.44	$1,042.40	$1,042.40