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	$220.88	12.297%	$248.0416	$248.04	$248.05	$248.00
Purchase #2	$131.63	12.146%	$147.6178	$147.62	$147.60	$147.60
Purchase #3	$185.86	13.330%	$210.6351	$210.64	$210.65	$210.60
Purchase #4	$10.52	13.172%	$11.9057	$11.91	$11.90	$11.90
Purchase #5	$166.41	5.695%	$175.887	$175.89	$175.90	$175.90
Purchase #6	$183.33	6.639%	$195.5013	$195.50	$195.50	$195.50
Purchase #7	$24.25	12.533%	$27.2893	$27.29	$27.30	$27.30
7 purchase totals =	$922.88		$1,016.8778	$1,016.89	$1,016.90	$1,016.80