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	$111.31	11.535%	$124.1496	$124.15	$124.15	$124.10
Purchase #2	$142.91	11.802%	$159.7762	$159.78	$159.80	$159.80
Purchase #3	$98.67	10.159%	$108.6939	$108.69	$108.70	$108.70
Purchase #4	$35.90	12.365%	$40.339	$40.34	$40.35	$40.30
Purchase #5	$139.73	6.195%	$148.3863	$148.39	$148.40	$148.40
Purchase #6	$53.92	9.245%	$58.9049	$58.90	$58.90	$58.90
Purchase #7	$156.72	12.496%	$176.3037	$176.30	$176.30	$176.30
7 purchase totals =	$739.16		$816.5536	$816.55	$816.60	$816.50