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	$57.54	10.761%	$63.7319	$63.73	$63.75	$63.70
Purchase #2	$207.36	3.729%	$215.0925	$215.09	$215.10	$215.10
Purchase #3	$209.76	11.104%	$233.0518	$233.05	$233.05	$233.10
Purchase #4	$19.49	7.546%	$20.9607	$20.96	$20.95	$21.00
Purchase #5	$238.69	4.788%	$250.1185	$250.12	$250.10	$250.10
Purchase #6	$87.86	4.363%	$91.6933	$91.69	$91.70	$91.70
Purchase #7	$111.78	6.265%	$118.783	$118.78	$118.80	$118.80
7 purchase totals =	$932.48		$993.4317	$993.42	$993.45	$993.50