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	$154.61	11.199%	$171.9248	$171.92	$171.90	$171.90
Purchase #2	$67.80	9.547%	$74.2729	$74.27	$74.25	$74.30
Purchase #3	$92.91	8.599%	$100.8993	$100.90	$100.90	$100.90
Purchase #4	$90.70	7.237%	$97.264	$97.26	$97.25	$97.30
Purchase #5	$153.57	6.650%	$163.7824	$163.78	$163.80	$163.80
Purchase #6	$57.78	13.599%	$65.6375	$65.64	$65.65	$65.60
Purchase #7	$90.70	10.229%	$99.9777	$99.98	$100.00	$100.00
7 purchase totals =	$708.07		$773.7586	$773.75	$773.75	$773.80