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	$139.71	11.109%	$155.2304	$155.23	$155.25	$155.20
Purchase #2	$121.62	5.864%	$128.7518	$128.75	$128.75	$128.80
Purchase #3	$102.74	8.763%	$111.7431	$111.74	$111.75	$111.70
Purchase #4	$250.65	5.369%	$264.1074	$264.11	$264.10	$264.10
Purchase #5	$141.29	10.535%	$156.1749	$156.17	$156.15	$156.20
Purchase #6	$102.63	8.737%	$111.5968	$111.60	$111.60	$111.60
Purchase #7	$185.89	9.788%	$204.0849	$204.08	$204.10	$204.10
7 purchase totals =	$1,044.53		$1,131.6893	$1,131.68	$1,131.70	$1,131.70