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	$28.45	7.150%	$30.4842	$30.48	$30.50	$30.50
Purchase #2	$222.40	12.660%	$250.5558	$250.56	$250.55	$250.60
Purchase #3	$29.84	6.198%	$31.6895	$31.69	$31.70	$31.70
Purchase #4	$189.43	13.578%	$215.1508	$215.15	$215.15	$215.20
Purchase #5	$108.85	13.123%	$123.1344	$123.13	$123.15	$123.10
Purchase #6	$107.70	11.664%	$120.2621	$120.26	$120.25	$120.30
Purchase #7	$242.38	11.282%	$269.7253	$269.73	$269.75	$269.70
7 purchase totals =	$929.05		$1,041.0021	$1,041.00	$1,041.05	$1,041.10