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	$119.35	13.374%	$135.3119	$135.31	$135.30	$135.30
Purchase #2	$188.69	10.403%	$208.3194	$208.32	$208.30	$208.30
Purchase #3	$97.83	7.454%	$105.1222	$105.12	$105.10	$105.10
Purchase #4	$65.52	9.312%	$71.6212	$71.62	$71.60	$71.60
Purchase #5	$54.73	11.274%	$60.9003	$60.90	$60.90	$60.90
Purchase #6	$56.86	3.591%	$58.9018	$58.90	$58.90	$58.90
Purchase #7	$145.47	9.566%	$159.3857	$159.39	$159.40	$159.40
7 purchase totals =	$728.45		$799.5625	$799.56	$799.50	$799.50