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	$131.46	11.434%	$146.4911	$146.49	$146.50	$146.50
Purchase #2	$80.73	5.263%	$84.9788	$84.98	$85.00	$85.00
Purchase #3	$47.82	8.449%	$51.8603	$51.86	$51.85	$51.90
Purchase #4	$53.57	7.326%	$57.4945	$57.49	$57.50	$57.50
Purchase #5	$41.85	13.250%	$47.3951	$47.40	$47.40	$47.40
Purchase #6	$88.46	10.688%	$97.9146	$97.91	$97.90	$97.90
Purchase #7	$39.38	6.375%	$41.8905	$41.89	$41.90	$41.90
7 purchase totals =	$483.27		$528.0249	$528.02	$528.05	$528.10