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	$250.50	11.467%	$279.2248	$279.22	$279.20	$279.20
Purchase #2	$46.46	7.289%	$49.8465	$49.85	$49.85	$49.80
Purchase #3	$126.98	3.233%	$131.0853	$131.09	$131.10	$131.10
Purchase #4	$164.98	3.864%	$171.3548	$171.35	$171.35	$171.40
Purchase #5	$204.92	3.679%	$212.459	$212.46	$212.45	$212.50
Purchase #6	$145.38	10.404%	$160.5053	$160.51	$160.50	$160.50
Purchase #7	$154.50	9.874%	$169.7553	$169.76	$169.75	$169.80
7 purchase totals =	$1,093.72		$1,174.2310	$1,174.24	$1,174.20	$1,174.30