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	$246.52	9.657%	$270.3264	$270.33	$270.35	$270.30
Purchase #2	$31.47	4.610%	$32.9208	$32.92	$32.90	$32.90
Purchase #3	$159.38	5.313%	$167.8479	$167.85	$167.85	$167.80
Purchase #4	$105.73	5.805%	$111.8676	$111.87	$111.85	$111.90
Purchase #5	$78.52	10.597%	$86.8408	$86.84	$86.85	$86.80
Purchase #6	$220.65	6.270%	$234.4848	$234.48	$234.50	$234.50
Purchase #7	$71.46	12.194%	$80.1738	$80.17	$80.15	$80.20
7 purchase totals =	$913.73		$984.4621	$984.46	$984.45	$984.40