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	$225.87	11.195%	$251.1561	$251.16	$251.15	$251.20
Purchase #2	$94.73	3.304%	$97.8599	$97.86	$97.85	$97.90
Purchase #3	$54.90	9.682%	$60.2154	$60.22	$60.20	$60.20
Purchase #4	$241.98	3.696%	$250.9236	$250.92	$250.90	$250.90
Purchase #5	$78.95	8.632%	$85.765	$85.77	$85.75	$85.80
Purchase #6	$29.99	11.228%	$33.3573	$33.36	$33.35	$33.40
Purchase #7	$69.40	3.849%	$72.0712	$72.07	$72.05	$72.10
7 purchase totals =	$795.82		$851.3485	$851.36	$851.25	$851.50