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	$141.43	3.411%	$146.2542	$146.25	$146.25	$146.30
Purchase #2	$182.65	3.533%	$189.103	$189.10	$189.10	$189.10
Purchase #3	$86.77	11.689%	$96.9125	$96.91	$96.90	$96.90
Purchase #4	$165.93	9.449%	$181.6087	$181.61	$181.60	$181.60
Purchase #5	$100.29	4.837%	$105.141	$105.14	$105.15	$105.10
Purchase #6	$9.56	5.629%	$10.0981	$10.10	$10.10	$10.10
Purchase #7	$180.63	6.520%	$192.4071	$192.41	$192.40	$192.40
7 purchase totals =	$867.26		$921.5246	$921.52	$921.50	$921.50