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	$58.86	10.453%	$65.0126	$65.01	$65.00	$65.00
Purchase #2	$165.53	12.585%	$186.362	$186.36	$186.35	$186.40
Purchase #3	$37.60	6.541%	$40.0594	$40.06	$40.05	$40.10
Purchase #4	$229.31	5.320%	$241.5093	$241.51	$241.50	$241.50
Purchase #5	$30.91	6.436%	$32.8994	$32.90	$32.90	$32.90
Purchase #6	$48.69	13.416%	$55.2223	$55.22	$55.20	$55.20
Purchase #7	$38.31	10.406%	$42.2965	$42.30	$42.30	$42.30
7 purchase totals =	$609.21		$663.3615	$663.36	$663.30	$663.40