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	$79.94	12.675%	$90.0724	$90.07	$90.05	$90.10
Purchase #2	$86.57	4.321%	$90.3107	$90.31	$90.30	$90.30
Purchase #3	$131.42	8.151%	$142.132	$142.13	$142.15	$142.10
Purchase #4	$28.63	6.766%	$30.5671	$30.57	$30.55	$30.60
Purchase #5	$93.92	7.861%	$101.3031	$101.30	$101.30	$101.30
Purchase #6	$215.87	8.587%	$234.4068	$234.41	$234.40	$234.40
Purchase #7	$231.70	13.843%	$263.7742	$263.77	$263.75	$263.80
7 purchase totals =	$868.05		$952.5663	$952.56	$952.50	$952.60