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	$57.80	8.344%	$62.6228	$62.62	$62.60	$62.60
Purchase #2	$133.41	12.865%	$150.5732	$150.57	$150.55	$150.60
Purchase #3	$120.84	8.532%	$131.1501	$131.15	$131.15	$131.20
Purchase #4	$131.83	4.392%	$137.62	$137.62	$137.60	$137.60
Purchase #5	$49.64	10.835%	$55.0185	$55.02	$55.00	$55.00
Purchase #6	$90.39	5.568%	$95.4229	$95.42	$95.40	$95.40
Purchase #7	$174.84	7.483%	$187.9233	$187.92	$187.90	$187.90
7 purchase totals =	$758.75		$820.3308	$820.32	$820.20	$820.30