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	$36.76	7.689%	$39.5865	$39.59	$39.60	$39.60
Purchase #2	$109.28	6.326%	$116.1931	$116.19	$116.20	$116.20
Purchase #3	$57.34	3.769%	$59.5011	$59.50	$59.50	$59.50
Purchase #4	$148.62	5.168%	$156.3007	$156.30	$156.30	$156.30
Purchase #5	$167.35	7.137%	$179.2938	$179.29	$179.30	$179.30
Purchase #6	$79.56	8.805%	$86.5653	$86.57	$86.55	$86.60
Purchase #7	$62.38	11.615%	$69.6254	$69.63	$69.65	$69.60
7 purchase totals =	$661.29		$707.0659	$707.07	$707.10	$707.10