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	$25.51	11.868%	$28.5375	$28.54	$28.55	$28.50
Purchase #2	$83.89	6.561%	$89.394	$89.39	$89.40	$89.40
Purchase #3	$178.78	11.240%	$198.8749	$198.87	$198.85	$198.90
Purchase #4	$131.69	3.282%	$136.0121	$136.01	$136.00	$136.00
Purchase #5	$237.78	5.543%	$250.9601	$250.96	$250.95	$251.00
Purchase #6	$139.78	13.491%	$158.6377	$158.64	$158.65	$158.60
Purchase #7	$179.78	3.338%	$185.7811	$185.78	$185.80	$185.80
7 purchase totals =	$977.21		$1,048.1974	$1,048.19	$1,048.20	$1,048.20