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	$25.38	11.443%	$28.2842	$28.28	$28.30	$28.30
Purchase #2	$159.47	7.721%	$171.7827	$171.78	$171.80	$171.80
Purchase #3	$213.42	8.354%	$231.2491	$231.25	$231.25	$231.20
Purchase #4	$171.38	10.621%	$189.5823	$189.58	$189.60	$189.60
Purchase #5	$210.95	10.524%	$233.1504	$233.15	$233.15	$233.20
Purchase #6	$200.34	7.531%	$215.4276	$215.43	$215.45	$215.40
Purchase #7	$21.34	8.389%	$23.1302	$23.13	$23.15	$23.10
7 purchase totals =	$1,002.28		$1,092.6065	$1,092.60	$1,092.70	$1,092.60