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	$103.68	5.646%	$109.5338	$109.53	$109.55	$109.50
Purchase #2	$69.88	4.530%	$73.0456	$73.05	$73.05	$73.00
Purchase #3	$52.74	12.219%	$59.1843	$59.18	$59.20	$59.20
Purchase #4	$94.53	8.516%	$102.5802	$102.58	$102.60	$102.60
Purchase #5	$64.85	13.755%	$73.7701	$73.77	$73.75	$73.80
Purchase #6	$38.88	7.165%	$41.6658	$41.67	$41.65	$41.70
Purchase #7	$115.59	10.227%	$127.4114	$127.41	$127.40	$127.40
7 purchase totals =	$540.15		$587.1912	$587.19	$587.20	$587.20