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	$44.46	13.119%	$50.2927	$50.29	$50.30	$50.30
Purchase #2	$5.79	5.809%	$6.1263	$6.13	$6.15	$6.10
Purchase #3	$119.29	3.208%	$123.1168	$123.12	$123.10	$123.10
Purchase #4	$74.66	5.166%	$78.5169	$78.52	$78.50	$78.50
Purchase #5	$186.50	13.504%	$211.685	$211.69	$211.70	$211.70
Purchase #6	$94.98	11.727%	$106.1183	$106.12	$106.10	$106.10
Purchase #7	$39.75	5.840%	$42.0714	$42.07	$42.05	$42.10
7 purchase totals =	$565.43		$617.9274	$617.94	$617.90	$617.90