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	$125.94	10.604%	$139.2947	$139.29	$139.30	$139.30
Purchase #2	$144.87	13.456%	$164.3637	$164.36	$164.35	$164.40
Purchase #3	$232.55	13.568%	$264.1024	$264.10	$264.10	$264.10
Purchase #4	$48.75	12.104%	$54.6507	$54.65	$54.65	$54.70
Purchase #5	$119.58	10.661%	$132.3284	$132.33	$132.35	$132.30
Purchase #6	$189.83	6.102%	$201.4134	$201.41	$201.40	$201.40
Purchase #7	$19.63	13.435%	$22.2673	$22.27	$22.25	$22.30
7 purchase totals =	$881.15		$978.4206	$978.41	$978.40	$978.50