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	$189.87	10.499%	$209.8045	$209.80	$209.80	$209.80
Purchase #2	$35.60	7.500%	$38.27	$38.27	$38.25	$38.30
Purchase #3	$83.88	10.142%	$92.3871	$92.39	$92.40	$92.40
Purchase #4	$55.94	5.317%	$58.9143	$58.91	$58.90	$58.90
Purchase #5	$244.28	12.759%	$275.4477	$275.45	$275.45	$275.40
Purchase #6	$171.26	4.874%	$179.6072	$179.61	$179.60	$179.60
Purchase #7	$42.62	7.295%	$45.7291	$45.73	$45.75	$45.70
7 purchase totals =	$823.45		$900.1599	$900.16	$900.15	$900.10