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	$144.34	6.374%	$153.5402	$153.54	$153.55	$153.50
Purchase #2	$169.99	12.713%	$191.6008	$191.60	$191.60	$191.60
Purchase #3	$221.76	13.177%	$250.9813	$250.98	$251.00	$251.00
Purchase #4	$56.52	8.847%	$61.5203	$61.52	$61.50	$61.50
Purchase #5	$162.41	13.174%	$183.8059	$183.81	$183.80	$183.80
Purchase #6	$93.98	6.219%	$99.8246	$99.82	$99.80	$99.80
Purchase #7	$171.61	8.400%	$186.0252	$186.03	$186.05	$186.00
7 purchase totals =	$1,020.61		$1,127.2983	$1,127.30	$1,127.30	$1,127.20