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	$39.62	7.495%	$42.5895	$42.59	$42.60	$42.60
Purchase #2	$133.72	6.470%	$142.3717	$142.37	$142.35	$142.40
Purchase #3	$19.96	11.349%	$22.2253	$22.23	$22.25	$22.20
Purchase #4	$70.31	8.216%	$76.0867	$76.09	$76.10	$76.10
Purchase #5	$78.56	5.417%	$82.8156	$82.82	$82.80	$82.80
Purchase #6	$40.64	6.592%	$43.319	$43.32	$43.30	$43.30
Purchase #7	$244.62	6.816%	$261.2933	$261.29	$261.30	$261.30
7 purchase totals =	$627.43		$670.7011	$670.71	$670.70	$670.70