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	$32.77	13.820%	$37.2988	$37.30	$37.30	$37.30
Purchase #2	$248.83	3.623%	$257.8451	$257.85	$257.85	$257.80
Purchase #3	$33.38	11.115%	$37.0902	$37.09	$37.10	$37.10
Purchase #4	$216.38	13.167%	$244.8708	$244.87	$244.85	$244.90
Purchase #5	$224.83	11.568%	$250.8383	$250.84	$250.85	$250.80
Purchase #6	$180.82	8.457%	$196.1119	$196.11	$196.10	$196.10
Purchase #7	$166.93	7.627%	$179.6618	$179.66	$179.65	$179.70
7 purchase totals =	$1,103.94		$1,203.7169	$1,203.72	$1,203.70	$1,203.70