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	$79.47	13.771%	$90.4138	$90.41	$90.40	$90.40
Purchase #2	$187.61	12.213%	$210.5228	$210.52	$210.50	$210.50
Purchase #3	$19.55	13.106%	$22.1122	$22.11	$22.10	$22.10
Purchase #4	$120.79	10.801%	$133.8365	$133.84	$133.85	$133.80
Purchase #5	$47.85	12.489%	$53.826	$53.83	$53.85	$53.80
Purchase #6	$49.88	6.336%	$53.0404	$53.04	$53.05	$53.00
Purchase #7	$63.52	12.228%	$71.2872	$71.29	$71.30	$71.30
7 purchase totals =	$568.67		$635.0389	$635.04	$635.05	$634.90