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	$71.60	11.158%	$79.5891	$79.59	$79.60	$79.60
Purchase #2	$125.91	6.457%	$134.04	$134.04	$134.05	$134.00
Purchase #3	$40.59	4.135%	$42.2684	$42.27	$42.25	$42.30
Purchase #4	$35.32	6.618%	$37.6575	$37.66	$37.65	$37.70
Purchase #5	$52.84	3.357%	$54.6138	$54.61	$54.60	$54.60
Purchase #6	$227.82	6.681%	$243.0407	$243.04	$243.05	$243.00
Purchase #7	$184.76	4.548%	$193.1629	$193.16	$193.15	$193.20
7 purchase totals =	$738.84		$784.3724	$784.37	$784.35	$784.40