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	$167.78	8.705%	$182.3852	$182.39	$182.40	$182.40
Purchase #2	$186.56	9.580%	$204.4324	$204.43	$204.45	$204.40
Purchase #3	$110.30	7.671%	$118.7611	$118.76	$118.75	$118.80
Purchase #4	$18.57	8.276%	$20.1069	$20.11	$20.10	$20.10
Purchase #5	$144.97	8.183%	$156.8329	$156.83	$156.85	$156.80
Purchase #6	$49.59	13.306%	$56.1884	$56.19	$56.20	$56.20
Purchase #7	$85.57	4.488%	$89.4104	$89.41	$89.40	$89.40
7 purchase totals =	$763.34		$828.1173	$828.12	$828.15	$828.10