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	$83.28	6.850%	$88.9847	$88.98	$89.00	$89.00
Purchase #2	$191.38	12.545%	$215.3886	$215.39	$215.40	$215.40
Purchase #3	$185.95	12.541%	$209.27	$209.27	$209.25	$209.30
Purchase #4	$72.47	9.683%	$79.4873	$79.49	$79.50	$79.50
Purchase #5	$247.42	11.534%	$275.9574	$275.96	$275.95	$276.00
Purchase #6	$234.90	8.170%	$254.0913	$254.09	$254.10	$254.10
Purchase #7	$166.83	13.614%	$189.5422	$189.54	$189.55	$189.50
7 purchase totals =	$1,182.23		$1,312.7215	$1,312.72	$1,312.75	$1,312.80