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	$6.74	10.740%	$7.4639	$7.46	$7.45	$7.50
Purchase #2	$9.54	10.344%	$10.5268	$10.53	$10.55	$10.50
Purchase #3	$191.92	8.435%	$208.1085	$208.11	$208.10	$208.10
Purchase #4	$170.86	8.518%	$185.4139	$185.41	$185.40	$185.40
Purchase #5	$140.44	11.106%	$156.0373	$156.04	$156.05	$156.00
Purchase #6	$138.94	9.782%	$152.5311	$152.53	$152.55	$152.50
Purchase #7	$134.65	12.788%	$151.869	$151.87	$151.85	$151.90
7 purchase totals =	$793.09		$871.9505	$871.95	$871.95	$871.90