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	$101.82	7.720%	$109.6805	$109.68	$109.70	$109.70
Purchase #2	$107.59	8.601%	$116.8438	$116.84	$116.85	$116.80
Purchase #3	$140.94	8.207%	$152.5069	$152.51	$152.50	$152.50
Purchase #4	$23.81	5.585%	$25.1398	$25.14	$25.15	$25.10
Purchase #5	$28.72	12.535%	$32.3201	$32.32	$32.30	$32.30
Purchase #6	$66.95	7.374%	$71.8869	$71.89	$71.90	$71.90
Purchase #7	$97.63	12.782%	$110.1091	$110.11	$110.10	$110.10
7 purchase totals =	$567.46		$618.4871	$618.49	$618.50	$618.40