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	$145.77	3.452%	$150.802	$150.80	$150.80	$150.80
Purchase #2	$57.31	12.321%	$64.3712	$64.37	$64.35	$64.40
Purchase #3	$94.35	12.205%	$105.8654	$105.87	$105.85	$105.90
Purchase #4	$125.98	8.258%	$136.3834	$136.38	$136.40	$136.40
Purchase #5	$43.29	9.205%	$47.2748	$47.27	$47.25	$47.30
Purchase #6	$180.29	5.543%	$190.2835	$190.28	$190.30	$190.30
Purchase #7	$150.70	7.819%	$162.4832	$162.48	$162.50	$162.50
7 purchase totals =	$797.69		$857.4635	$857.45	$857.45	$857.60