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	$50.85	6.719%	$54.2666	$54.27	$54.25	$54.30
Purchase #2	$143.89	12.703%	$162.1683	$162.17	$162.15	$162.20
Purchase #3	$74.98	9.732%	$82.2771	$82.28	$82.30	$82.30
Purchase #4	$22.62	9.460%	$24.7599	$24.76	$24.75	$24.80
Purchase #5	$134.57	11.835%	$150.4964	$150.50	$150.50	$150.50
Purchase #6	$150.33	13.718%	$170.9523	$170.95	$170.95	$171.00
Purchase #7	$130.27	8.607%	$141.4823	$141.48	$141.50	$141.50
7 purchase totals =	$707.51		$786.4029	$786.41	$786.40	$786.60