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	$91.44	8.816%	$99.5014	$99.50	$99.50	$99.50
Purchase #2	$138.64	11.340%	$154.3618	$154.36	$154.35	$154.40
Purchase #3	$222.61	13.803%	$253.3369	$253.34	$253.35	$253.30
Purchase #4	$148.98	5.201%	$156.7284	$156.73	$156.75	$156.70
Purchase #5	$103.32	11.155%	$114.8453	$114.85	$114.85	$114.80
Purchase #6	$121.68	8.629%	$132.1798	$132.18	$132.20	$132.20
Purchase #7	$245.79	6.398%	$261.5156	$261.52	$261.50	$261.50
7 purchase totals =	$1,072.46		$1,172.4692	$1,172.48	$1,172.50	$1,172.40