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	$7.48	12.507%	$8.4155	$8.42	$8.40	$8.40
Purchase #2	$9.50	12.483%	$10.6859	$10.69	$10.70	$10.70
Purchase #3	$48.58	3.569%	$50.3138	$50.31	$50.30	$50.30
Purchase #4	$40.51	5.814%	$42.8653	$42.87	$42.85	$42.90
Purchase #5	$229.32	8.799%	$249.4979	$249.50	$249.50	$249.50
Purchase #6	$177.93	12.653%	$200.4435	$200.44	$200.45	$200.40
Purchase #7	$126.31	12.871%	$142.5674	$142.57	$142.55	$142.60
7 purchase totals =	$639.63		$704.7893	$704.80	$704.75	$704.80