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	$8.84	5.405%	$9.3178	$9.32	$9.30	$9.30
Purchase #2	$30.93	5.493%	$32.629	$32.63	$32.65	$32.60
Purchase #3	$43.33	11.751%	$48.4217	$48.42	$48.40	$48.40
Purchase #4	$171.34	10.415%	$189.1851	$189.19	$189.20	$189.20
Purchase #5	$100.66	10.322%	$111.0501	$111.05	$111.05	$111.10
Purchase #6	$82.86	8.543%	$89.9387	$89.94	$89.95	$89.90
Purchase #7	$48.69	12.774%	$54.9097	$54.91	$54.90	$54.90
7 purchase totals =	$486.65		$535.4521	$535.46	$535.45	$535.40