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	$81.78	8.616%	$88.8262	$88.83	$88.85	$88.80
Purchase #2	$242.38	10.459%	$267.7305	$267.73	$267.75	$267.70
Purchase #3	$198.94	11.820%	$222.4547	$222.45	$222.45	$222.50
Purchase #4	$61.83	13.104%	$69.9322	$69.93	$69.95	$69.90
Purchase #5	$178.43	12.357%	$200.4786	$200.48	$200.50	$200.50
Purchase #6	$56.63	4.410%	$59.1274	$59.13	$59.15	$59.10
Purchase #7	$239.38	11.209%	$266.2121	$266.21	$266.20	$266.20
7 purchase totals =	$1,059.37		$1,174.7617	$1,174.76	$1,174.85	$1,174.70