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	$90.55	9.770%	$99.3967	$99.40	$99.40	$99.40
Purchase #2	$104.63	11.740%	$116.9136	$116.91	$116.90	$116.90
Purchase #3	$179.46	13.636%	$203.9312	$203.93	$203.95	$203.90
Purchase #4	$152.40	9.210%	$166.436	$166.44	$166.45	$166.40
Purchase #5	$56.41	11.501%	$62.8977	$62.90	$62.90	$62.90
Purchase #6	$225.74	5.687%	$238.5778	$238.58	$238.60	$238.60
Purchase #7	$201.65	5.378%	$212.4947	$212.49	$212.50	$212.50
7 purchase totals =	$1,010.84		$1,100.6477	$1,100.65	$1,100.70	$1,100.60