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	$182.73	3.370%	$188.888	$188.89	$188.90	$188.90
Purchase #2	$39.94	8.178%	$43.2063	$43.21	$43.20	$43.20
Purchase #3	$172.75	13.796%	$196.5826	$196.58	$196.60	$196.60
Purchase #4	$34.74	7.162%	$37.2281	$37.23	$37.25	$37.20
Purchase #5	$46.74	11.584%	$52.1544	$52.15	$52.15	$52.20
Purchase #6	$47.80	12.761%	$53.8998	$53.90	$53.90	$53.90
Purchase #7	$200.79	9.389%	$219.6422	$219.64	$219.65	$219.60
7 purchase totals =	$725.49		$791.6014	$791.60	$791.65	$791.60