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	$247.34	13.268%	$280.1571	$280.16	$280.15	$280.20
Purchase #2	$152.26	9.532%	$166.7734	$166.77	$166.75	$166.80
Purchase #3	$230.91	13.443%	$261.9512	$261.95	$261.95	$262.00
Purchase #4	$52.33	12.860%	$59.0596	$59.06	$59.05	$59.10
Purchase #5	$209.53	6.700%	$223.5685	$223.57	$223.55	$223.60
Purchase #6	$154.46	13.852%	$175.8558	$175.86	$175.85	$175.90
Purchase #7	$162.78	6.274%	$172.9928	$172.99	$173.00	$173.00
7 purchase totals =	$1,209.61		$1,340.3584	$1,340.36	$1,340.30	$1,340.60