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	$76.71	10.726%	$84.9379	$84.94	$84.95	$84.90
Purchase #2	$82.56	5.665%	$87.237	$87.24	$87.25	$87.20
Purchase #3	$25.94	8.731%	$28.2048	$28.20	$28.20	$28.20
Purchase #4	$211.58	13.466%	$240.0714	$240.07	$240.05	$240.10
Purchase #5	$96.78	3.497%	$100.1644	$100.16	$100.15	$100.20
Purchase #6	$207.66	7.275%	$222.7673	$222.77	$222.75	$222.80
Purchase #7	$53.38	12.284%	$59.9372	$59.94	$59.95	$59.90
7 purchase totals =	$754.61		$823.3200	$823.32	$823.30	$823.30