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	$18.66	7.711%	$20.0989	$20.10	$20.10	$20.10
Purchase #2	$76.65	6.320%	$81.4943	$81.49	$81.50	$81.50
Purchase #3	$142.81	13.711%	$162.3907	$162.39	$162.40	$162.40
Purchase #4	$66.86	7.755%	$72.045	$72.05	$72.05	$72.00
Purchase #5	$235.65	13.647%	$267.8092	$267.81	$267.80	$267.80
Purchase #6	$76.71	8.613%	$83.317	$83.32	$83.30	$83.30
Purchase #7	$245.86	9.231%	$268.5553	$268.56	$268.55	$268.60
7 purchase totals =	$863.20		$955.7104	$955.72	$955.70	$955.70