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	$158.78	13.188%	$179.7199	$179.72	$179.70	$179.70
Purchase #2	$217.38	4.270%	$226.6621	$226.66	$226.65	$226.70
Purchase #3	$144.69	12.524%	$162.811	$162.81	$162.80	$162.80
Purchase #4	$79.99	13.153%	$90.5111	$90.51	$90.50	$90.50
Purchase #5	$199.33	12.195%	$223.6383	$223.64	$223.65	$223.60
Purchase #6	$27.53	4.589%	$28.7934	$28.79	$28.80	$28.80
Purchase #7	$247.51	8.107%	$267.5756	$267.58	$267.60	$267.60
7 purchase totals =	$1,075.21		$1,179.7114	$1,179.71	$1,179.70	$1,179.70