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	$111.89	3.256%	$115.5331	$115.53	$115.55	$115.50
Purchase #2	$110.33	3.736%	$114.4519	$114.45	$114.45	$114.50
Purchase #3	$173.46	3.733%	$179.9353	$179.94	$179.95	$179.90
Purchase #4	$186.98	4.528%	$195.4465	$195.45	$195.45	$195.40
Purchase #5	$205.45	13.562%	$233.3131	$233.31	$233.30	$233.30
Purchase #6	$40.67	3.524%	$42.1032	$42.10	$42.10	$42.10
Purchase #7	$32.31	5.469%	$34.077	$34.08	$34.10	$34.10
7 purchase totals =	$861.09		$914.8601	$914.86	$914.90	$914.80