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	$54.56	3.466%	$56.451	$56.45	$56.45	$56.50
Purchase #2	$49.28	5.334%	$51.9086	$51.91	$51.90	$51.90
Purchase #3	$179.91	5.863%	$190.4581	$190.46	$190.45	$190.50
Purchase #4	$181.61	9.292%	$198.4852	$198.49	$198.50	$198.50
Purchase #5	$123.36	5.736%	$130.4359	$130.44	$130.45	$130.40
Purchase #6	$170.37	9.776%	$187.0254	$187.03	$187.05	$187.00
Purchase #7	$96.83	12.730%	$109.1565	$109.16	$109.15	$109.20
7 purchase totals =	$855.92		$923.9207	$923.94	$923.95	$924.00