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	$137.53	10.171%	$151.5182	$151.52	$151.50	$151.50
Purchase #2	$48.27	13.588%	$54.8289	$54.83	$54.85	$54.80
Purchase #3	$86.59	7.615%	$93.1838	$93.18	$93.20	$93.20
Purchase #4	$154.88	10.484%	$171.1176	$171.12	$171.10	$171.10
Purchase #5	$35.61	13.824%	$40.5327	$40.53	$40.55	$40.50
Purchase #6	$156.45	3.780%	$162.3638	$162.36	$162.35	$162.40
Purchase #7	$115.34	11.675%	$128.8059	$128.81	$128.80	$128.80
7 purchase totals =	$734.67		$802.3509	$802.35	$802.35	$802.30