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	$150.69	11.112%	$167.4347	$167.43	$167.45	$167.40
Purchase #2	$97.37	7.674%	$104.8422	$104.84	$104.85	$104.80
Purchase #3	$18.77	7.374%	$20.1541	$20.15	$20.15	$20.20
Purchase #4	$28.27	12.495%	$31.8023	$31.80	$31.80	$31.80
Purchase #5	$173.74	6.713%	$185.4032	$185.40	$185.40	$185.40
Purchase #6	$221.98	3.405%	$229.5384	$229.54	$229.55	$229.50
Purchase #7	$96.41	4.441%	$100.6916	$100.69	$100.70	$100.70
7 purchase totals =	$787.23		$839.8665	$839.85	$839.90	$839.80