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	$239.76	7.385%	$257.4663	$257.47	$257.45	$257.50
Purchase #2	$226.30	9.153%	$247.0132	$247.01	$247.00	$247.00
Purchase #3	$116.46	9.754%	$127.8195	$127.82	$127.80	$127.80
Purchase #4	$121.83	4.807%	$127.6864	$127.69	$127.70	$127.70
Purchase #5	$152.81	7.419%	$164.147	$164.15	$164.15	$164.10
Purchase #6	$76.31	6.803%	$81.5014	$81.50	$81.50	$81.50
Purchase #7	$236.86	11.777%	$264.755	$264.76	$264.75	$264.80
7 purchase totals =	$1,170.33		$1,270.3888	$1,270.40	$1,270.35	$1,270.40