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	$118.32	5.188%	$124.4584	$124.46	$124.45	$124.50
Purchase #2	$180.84	7.450%	$194.3126	$194.31	$194.30	$194.30
Purchase #3	$45.74	6.276%	$48.6106	$48.61	$48.60	$48.60
Purchase #4	$143.70	3.214%	$148.3185	$148.32	$148.30	$148.30
Purchase #5	$18.40	11.647%	$20.543	$20.54	$20.55	$20.50
Purchase #6	$39.41	9.166%	$43.0223	$43.02	$43.00	$43.00
Purchase #7	$57.35	10.360%	$63.2915	$63.29	$63.30	$63.30
7 purchase totals =	$603.76		$642.5569	$642.55	$642.50	$642.50