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	$70.32	10.262%	$77.5362	$77.54	$77.55	$77.50
Purchase #2	$215.55	6.663%	$229.9121	$229.91	$229.90	$229.90
Purchase #3	$41.90	9.628%	$45.9341	$45.93	$45.95	$45.90
Purchase #4	$48.82	6.181%	$51.8376	$51.84	$51.85	$51.80
Purchase #5	$233.83	7.119%	$250.4764	$250.48	$250.50	$250.50
Purchase #6	$113.49	7.121%	$121.5716	$121.57	$121.55	$121.60
Purchase #7	$127.83	7.854%	$137.8698	$137.87	$137.85	$137.90
7 purchase totals =	$851.74		$915.1378	$915.14	$915.15	$915.10