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	$146.59	13.271%	$166.044	$166.04	$166.05	$166.00
Purchase #2	$226.81	7.488%	$243.7935	$243.79	$243.80	$243.80
Purchase #3	$200.81	11.237%	$223.375	$223.38	$223.40	$223.40
Purchase #4	$208.92	9.849%	$229.4965	$229.50	$229.50	$229.50
Purchase #5	$44.28	4.421%	$46.2376	$46.24	$46.25	$46.20
Purchase #6	$174.68	12.677%	$196.8242	$196.82	$196.80	$196.80
Purchase #7	$108.66	6.535%	$115.7609	$115.76	$115.75	$115.80
7 purchase totals =	$1,110.75		$1,221.5317	$1,221.53	$1,221.55	$1,221.50