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	$153.49	7.175%	$164.5029	$164.50	$164.50	$164.50
Purchase #2	$5.87	12.190%	$6.5856	$6.59	$6.60	$6.60
Purchase #3	$36.93	6.442%	$39.309	$39.31	$39.30	$39.30
Purchase #4	$209.76	3.764%	$217.6554	$217.66	$217.65	$217.70
Purchase #5	$214.63	13.374%	$243.3346	$243.33	$243.35	$243.30
Purchase #6	$217.66	10.365%	$240.2205	$240.22	$240.20	$240.20
Purchase #7	$54.38	9.434%	$59.5102	$59.51	$59.50	$59.50
7 purchase totals =	$892.72		$971.1182	$971.12	$971.10	$971.10