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	$245.99	4.343%	$256.6733	$256.67	$256.65	$256.70
Purchase #2	$53.41	5.843%	$56.5307	$56.53	$56.55	$56.50
Purchase #3	$165.34	13.690%	$187.975	$187.98	$188.00	$188.00
Purchase #4	$200.25	11.853%	$223.9856	$223.99	$224.00	$224.00
Purchase #5	$41.73	3.433%	$43.1626	$43.16	$43.15	$43.20
Purchase #6	$39.85	7.713%	$42.9236	$42.92	$42.90	$42.90
Purchase #7	$222.65	8.626%	$241.8558	$241.86	$241.85	$241.90
7 purchase totals =	$969.22		$1,053.1066	$1,053.11	$1,053.10	$1,053.20