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	$243.41	6.307%	$258.7619	$258.76	$258.75	$258.80
Purchase #2	$222.64	12.800%	$251.1379	$251.14	$251.15	$251.10
Purchase #3	$162.64	11.537%	$181.4038	$181.40	$181.40	$181.40
Purchase #4	$71.82	11.204%	$79.8667	$79.87	$79.85	$79.90
Purchase #5	$152.31	12.475%	$171.3107	$171.31	$171.30	$171.30
Purchase #6	$32.73	7.715%	$35.2551	$35.26	$35.25	$35.30
Purchase #7	$181.69	8.202%	$196.5922	$196.59	$196.60	$196.60
7 purchase totals =	$1,067.24		$1,174.3283	$1,174.33	$1,174.30	$1,174.40