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	$46.71	5.140%	$49.1109	$49.11	$49.10	$49.10
Purchase #2	$207.79	12.598%	$233.9674	$233.97	$233.95	$234.00
Purchase #3	$52.78	13.170%	$59.7311	$59.73	$59.75	$59.70
Purchase #4	$192.43	11.799%	$215.1348	$215.13	$215.15	$215.10
Purchase #5	$139.40	12.219%	$156.4333	$156.43	$156.45	$156.40
Purchase #6	$30.62	8.813%	$33.3185	$33.32	$33.30	$33.30
Purchase #7	$96.79	13.377%	$109.7376	$109.74	$109.75	$109.70
7 purchase totals =	$766.52		$857.4336	$857.43	$857.45	$857.30