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	$19.47	9.394%	$21.299	$21.30	$21.30	$21.30
Purchase #2	$129.75	3.170%	$133.8631	$133.86	$133.85	$133.90
Purchase #3	$207.63	5.702%	$219.4691	$219.47	$219.45	$219.50
Purchase #4	$133.41	12.457%	$150.0289	$150.03	$150.05	$150.00
Purchase #5	$148.30	12.106%	$166.2532	$166.25	$166.25	$166.30
Purchase #6	$67.25	6.179%	$71.4054	$71.41	$71.40	$71.40
Purchase #7	$223.50	7.456%	$240.1642	$240.16	$240.15	$240.20
7 purchase totals =	$929.31		$1,002.4829	$1,002.48	$1,002.45	$1,002.60