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	$239.79	10.466%	$264.8864	$264.89	$264.90	$264.90
Purchase #2	$108.31	11.398%	$120.6552	$120.66	$120.65	$120.70
Purchase #3	$62.93	7.334%	$67.5453	$67.55	$67.55	$67.50
Purchase #4	$199.50	9.294%	$218.0415	$218.04	$218.05	$218.00
Purchase #5	$110.72	12.733%	$124.818	$124.82	$124.80	$124.80
Purchase #6	$167.32	10.212%	$184.4067	$184.41	$184.40	$184.40
Purchase #7	$91.64	13.503%	$104.0141	$104.01	$104.00	$104.00
7 purchase totals =	$980.21		$1,084.3672	$1,084.38	$1,084.35	$1,084.30