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	$71.88	12.829%	$81.1015	$81.10	$81.10	$81.10
Purchase #2	$32.44	11.534%	$36.1816	$36.18	$36.20	$36.20
Purchase #3	$59.51	3.667%	$61.6922	$61.69	$61.70	$61.70
Purchase #4	$39.97	11.473%	$44.5558	$44.56	$44.55	$44.60
Purchase #5	$72.93	7.613%	$78.4822	$78.48	$78.50	$78.50
Purchase #6	$5.92	4.765%	$6.2021	$6.20	$6.20	$6.20
Purchase #7	$133.92	6.490%	$142.6114	$142.61	$142.60	$142.60
7 purchase totals =	$416.57		$450.8268	$450.82	$450.85	$450.90