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	$243.26	4.537%	$254.2967	$254.30	$254.30	$254.30
Purchase #2	$35.73	10.377%	$39.4377	$39.44	$39.45	$39.40
Purchase #3	$223.76	3.663%	$231.9563	$231.96	$231.95	$232.00
Purchase #4	$161.65	6.595%	$172.3108	$172.31	$172.30	$172.30
Purchase #5	$107.55	6.104%	$114.1149	$114.11	$114.10	$114.10
Purchase #6	$103.39	12.498%	$116.3117	$116.31	$116.30	$116.30
Purchase #7	$135.37	12.752%	$152.6324	$152.63	$152.65	$152.60
7 purchase totals =	$1,010.71		$1,081.0605	$1,081.06	$1,081.05	$1,081.00