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	$167.69	5.218%	$176.4401	$176.44	$176.45	$176.40
Purchase #2	$54.36	11.225%	$60.4619	$60.46	$60.45	$60.50
Purchase #3	$173.43	13.478%	$196.8049	$196.80	$196.80	$196.80
Purchase #4	$87.51	9.424%	$95.7569	$95.76	$95.75	$95.80
Purchase #5	$64.88	9.329%	$70.9327	$70.93	$70.95	$70.90
Purchase #6	$224.80	12.748%	$253.4575	$253.46	$253.45	$253.50
Purchase #7	$80.43	11.700%	$89.8403	$89.84	$89.85	$89.80
7 purchase totals =	$853.10		$943.6943	$943.69	$943.70	$943.70