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	$204.30	13.331%	$231.5352	$231.54	$231.55	$231.50
Purchase #2	$250.49	11.194%	$278.5299	$278.53	$278.55	$278.50
Purchase #3	$183.30	12.607%	$206.4086	$206.41	$206.40	$206.40
Purchase #4	$35.99	9.740%	$39.4954	$39.50	$39.50	$39.50
Purchase #5	$55.90	12.574%	$62.9289	$62.93	$62.95	$62.90
Purchase #6	$152.41	11.503%	$169.9417	$169.94	$169.95	$169.90
Purchase #7	$25.44	13.323%	$28.8294	$28.83	$28.85	$28.80
7 purchase totals =	$907.83		$1,017.6691	$1,017.68	$1,017.75	$1,017.50