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	$86.51	6.325%	$91.9818	$91.98	$92.00	$92.00
Purchase #2	$55.62	7.629%	$59.8632	$59.86	$59.85	$59.90
Purchase #3	$82.48	10.300%	$90.9754	$90.98	$91.00	$91.00
Purchase #4	$217.90	12.479%	$245.0917	$245.09	$245.10	$245.10
Purchase #5	$172.50	6.247%	$183.2761	$183.28	$183.30	$183.30
Purchase #6	$67.49	12.403%	$75.8608	$75.86	$75.85	$75.90
Purchase #7	$127.34	10.419%	$140.6076	$140.61	$140.60	$140.60
7 purchase totals =	$809.84		$887.6566	$887.66	$887.70	$887.80