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	$27.69	10.544%	$30.6096	$30.61	$30.60	$30.60
Purchase #2	$56.86	9.211%	$62.0974	$62.10	$62.10	$62.10
Purchase #3	$29.63	10.539%	$32.7527	$32.75	$32.75	$32.80
Purchase #4	$158.68	13.377%	$179.9066	$179.91	$179.90	$179.90
Purchase #5	$80.95	10.110%	$89.134	$89.13	$89.15	$89.10
Purchase #6	$147.29	12.788%	$166.1254	$166.13	$166.15	$166.10
Purchase #7	$169.54	9.472%	$185.5988	$185.60	$185.60	$185.60
7 purchase totals =	$670.64		$746.2245	$746.23	$746.25	$746.20