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	$46.86	11.645%	$52.3168	$52.32	$52.30	$52.30
Purchase #2	$18.94	8.565%	$20.5622	$20.56	$20.55	$20.60
Purchase #3	$171.86	10.341%	$189.632	$189.63	$189.65	$189.60
Purchase #4	$91.72	5.556%	$96.816	$96.82	$96.80	$96.80
Purchase #5	$195.87	9.505%	$214.4874	$214.49	$214.50	$214.50
Purchase #6	$208.85	3.652%	$216.4772	$216.48	$216.50	$216.50
Purchase #7	$47.33	9.265%	$51.7151	$51.72	$51.70	$51.70
7 purchase totals =	$781.43		$842.0067	$842.02	$842.00	$842.00