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	$70.60	11.582%	$78.7769	$78.78	$78.80	$78.80
Purchase #2	$246.31	9.109%	$268.7464	$268.75	$268.75	$268.70
Purchase #3	$250.38	7.623%	$269.4665	$269.47	$269.45	$269.50
Purchase #4	$123.84	12.811%	$139.7051	$139.71	$139.70	$139.70
Purchase #5	$123.89	11.568%	$138.2216	$138.22	$138.20	$138.20
Purchase #6	$141.46	12.142%	$158.6361	$158.64	$158.65	$158.60
Purchase #7	$250.35	8.654%	$272.0153	$272.02	$272.00	$272.00
7 purchase totals =	$1,206.83		$1,325.5679	$1,325.59	$1,325.55	$1,325.50