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	$61.53	13.375%	$69.7596	$69.76	$69.75	$69.80
Purchase #2	$235.39	9.565%	$257.9051	$257.91	$257.90	$257.90
Purchase #3	$45.72	6.204%	$48.5565	$48.56	$48.55	$48.60
Purchase #4	$200.46	12.435%	$225.3872	$225.39	$225.40	$225.40
Purchase #5	$137.49	10.861%	$152.4228	$152.42	$152.40	$152.40
Purchase #6	$21.34	4.871%	$22.3795	$22.38	$22.40	$22.40
Purchase #7	$67.94	6.658%	$72.4634	$72.46	$72.45	$72.50
7 purchase totals =	$769.87		$848.8741	$848.88	$848.85	$849.00