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	$12.65	5.391%	$13.332	$13.33	$13.35	$13.30
Purchase #2	$129.81	7.168%	$139.1148	$139.11	$139.10	$139.10
Purchase #3	$63.53	12.399%	$71.4071	$71.41	$71.40	$71.40
Purchase #4	$88.70	9.204%	$96.8639	$96.86	$96.85	$96.90
Purchase #5	$19.74	6.180%	$20.9599	$20.96	$20.95	$21.00
Purchase #6	$80.49	11.765%	$89.9596	$89.96	$89.95	$90.00
Purchase #7	$173.39	13.534%	$196.8566	$196.86	$196.85	$196.90
7 purchase totals =	$568.31		$628.4939	$628.49	$628.45	$628.60