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	$83.54	7.517%	$89.8197	$89.82	$89.80	$89.80
Purchase #2	$86.31	4.228%	$89.9592	$89.96	$89.95	$90.00
Purchase #3	$219.72	12.615%	$247.4377	$247.44	$247.45	$247.40
Purchase #4	$17.76	9.318%	$19.4149	$19.41	$19.40	$19.40
Purchase #5	$46.62	11.271%	$51.8745	$51.87	$51.85	$51.90
Purchase #6	$82.75	12.166%	$92.8174	$92.82	$92.80	$92.80
Purchase #7	$10.99	6.373%	$11.6904	$11.69	$11.70	$11.70
7 purchase totals =	$547.69		$603.0138	$603.01	$602.95	$603.00