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	$131.80	4.598%	$137.8602	$137.86	$137.85	$137.90
Purchase #2	$173.92	10.742%	$192.6025	$192.60	$192.60	$192.60
Purchase #3	$59.70	10.674%	$66.0724	$66.07	$66.05	$66.10
Purchase #4	$28.28	13.360%	$32.0582	$32.06	$32.05	$32.10
Purchase #5	$182.41	3.299%	$188.4277	$188.43	$188.45	$188.40
Purchase #6	$96.64	10.539%	$106.8249	$106.82	$106.80	$106.80
Purchase #7	$36.88	8.787%	$40.1206	$40.12	$40.10	$40.10
7 purchase totals =	$709.63		$763.9665	$763.96	$763.90	$764.00