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	$116.98	10.697%	$129.4934	$129.49	$129.50	$129.50
Purchase #2	$159.78	5.109%	$167.9432	$167.94	$167.95	$167.90
Purchase #3	$46.93	7.457%	$50.4296	$50.43	$50.45	$50.40
Purchase #4	$128.54	3.665%	$133.251	$133.25	$133.25	$133.30
Purchase #5	$19.38	12.843%	$21.869	$21.87	$21.85	$21.90
Purchase #6	$228.73	11.289%	$254.5513	$254.55	$254.55	$254.60
Purchase #7	$72.77	8.383%	$78.8703	$78.87	$78.85	$78.90
7 purchase totals =	$773.11		$836.4078	$836.40	$836.40	$836.50