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	$166.44	9.528%	$182.2984	$182.30	$182.30	$182.30
Purchase #2	$193.37	11.604%	$215.8087	$215.81	$215.80	$215.80
Purchase #3	$72.93	10.228%	$80.3893	$80.39	$80.40	$80.40
Purchase #4	$67.28	6.331%	$71.5395	$71.54	$71.55	$71.50
Purchase #5	$170.90	10.541%	$188.9146	$188.91	$188.90	$188.90
Purchase #6	$101.94	12.675%	$114.8609	$114.86	$114.85	$114.90
Purchase #7	$49.26	9.575%	$53.9766	$53.98	$54.00	$54.00
7 purchase totals =	$822.12		$907.7880	$907.79	$907.80	$907.80