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	$179.73	13.163%	$203.3879	$203.39	$203.40	$203.40
Purchase #2	$187.59	10.431%	$207.1575	$207.16	$207.15	$207.20
Purchase #3	$223.55	6.360%	$237.7678	$237.77	$237.75	$237.80
Purchase #4	$79.37	12.691%	$89.4428	$89.44	$89.45	$89.40
Purchase #5	$134.82	9.378%	$147.4634	$147.46	$147.45	$147.50
Purchase #6	$137.31	6.424%	$146.1308	$146.13	$146.15	$146.10
Purchase #7	$37.45	10.738%	$41.4714	$41.47	$41.45	$41.50
7 purchase totals =	$979.82		$1,072.8216	$1,072.82	$1,072.80	$1,072.90