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	$154.51	11.201%	$171.8167	$171.82	$171.80	$171.80
Purchase #2	$30.37	9.863%	$33.3654	$33.37	$33.35	$33.40
Purchase #3	$74.42	8.794%	$80.9645	$80.96	$80.95	$81.00
Purchase #4	$182.54	12.118%	$204.6602	$204.66	$204.65	$204.70
Purchase #5	$38.72	3.256%	$39.9807	$39.98	$40.00	$40.00
Purchase #6	$57.61	6.800%	$61.5275	$61.53	$61.55	$61.50
Purchase #7	$240.31	5.515%	$253.5631	$253.56	$253.55	$253.60
7 purchase totals =	$778.48		$845.8781	$845.88	$845.85	$846.00