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	$167.81	6.410%	$178.5666	$178.57	$178.55	$178.60
Purchase #2	$99.44	12.384%	$111.7546	$111.75	$111.75	$111.80
Purchase #3	$157.90	11.414%	$175.9227	$175.92	$175.90	$175.90
Purchase #4	$23.94	12.274%	$26.8784	$26.88	$26.90	$26.90
Purchase #5	$181.47	8.223%	$196.3923	$196.39	$196.40	$196.40
Purchase #6	$61.99	7.370%	$66.5587	$66.56	$66.55	$66.60
Purchase #7	$76.65	11.382%	$85.3743	$85.37	$85.35	$85.40
7 purchase totals =	$769.20		$841.4476	$841.44	$841.40	$841.60