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	$52.25	8.761%	$56.8276	$56.83	$56.85	$56.80
Purchase #2	$41.31	10.483%	$45.6405	$45.64	$45.65	$45.60
Purchase #3	$96.42	7.754%	$103.8964	$103.90	$103.90	$103.90
Purchase #4	$247.75	13.240%	$280.5521	$280.55	$280.55	$280.60
Purchase #5	$10.90	9.272%	$11.9106	$11.91	$11.90	$11.90
Purchase #6	$209.72	5.647%	$221.5629	$221.56	$221.55	$221.60
Purchase #7	$122.98	6.632%	$131.136	$131.14	$131.15	$131.10
7 purchase totals =	$781.33		$851.5261	$851.53	$851.55	$851.50