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	$170.52	8.802%	$185.5292	$185.53	$185.55	$185.50
Purchase #2	$80.48	4.226%	$83.8811	$83.88	$83.90	$83.90
Purchase #3	$111.88	6.613%	$119.2786	$119.28	$119.30	$119.30
Purchase #4	$87.88	11.843%	$98.2876	$98.29	$98.30	$98.30
Purchase #5	$214.34	9.308%	$234.2908	$234.29	$234.30	$234.30
Purchase #6	$107.77	7.347%	$115.6879	$115.69	$115.70	$115.70
Purchase #7	$135.56	6.837%	$144.8282	$144.83	$144.85	$144.80
7 purchase totals =	$908.43		$981.7834	$981.79	$981.90	$981.80