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	$104.27	13.274%	$118.1108	$118.11	$118.10	$118.10
Purchase #2	$171.56	13.399%	$194.5473	$194.55	$194.55	$194.50
Purchase #3	$168.68	13.375%	$191.241	$191.24	$191.25	$191.20
Purchase #4	$18.56	10.564%	$20.5207	$20.52	$20.50	$20.50
Purchase #5	$237.30	10.245%	$261.6114	$261.61	$261.60	$261.60
Purchase #6	$173.33	3.579%	$179.5335	$179.53	$179.55	$179.50
Purchase #7	$43.78	10.591%	$48.4167	$48.42	$48.40	$48.40
7 purchase totals =	$917.48		$1,013.9814	$1,013.98	$1,013.95	$1,013.80