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	$7.51	13.522%	$8.5255	$8.53	$8.55	$8.50
Purchase #2	$242.31	10.736%	$268.3244	$268.32	$268.30	$268.30
Purchase #3	$111.32	7.336%	$119.4864	$119.49	$119.50	$119.50
Purchase #4	$18.43	8.589%	$20.013	$20.01	$20.00	$20.00
Purchase #5	$139.44	8.769%	$151.6675	$151.67	$151.65	$151.70
Purchase #6	$40.69	11.781%	$45.4837	$45.48	$45.50	$45.50
Purchase #7	$159.33	12.204%	$178.7746	$178.77	$178.75	$178.80
7 purchase totals =	$719.03		$792.2751	$792.27	$792.25	$792.30