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	$249.67	4.495%	$260.8927	$260.89	$260.90	$260.90
Purchase #2	$85.64	9.846%	$94.0721	$94.07	$94.05	$94.10
Purchase #3	$73.62	13.505%	$83.5624	$83.56	$83.55	$83.60
Purchase #4	$29.68	6.780%	$31.6923	$31.69	$31.70	$31.70
Purchase #5	$100.32	9.543%	$109.8935	$109.89	$109.90	$109.90
Purchase #6	$39.62	4.434%	$41.3768	$41.38	$41.40	$41.40
Purchase #7	$124.88	10.303%	$137.7464	$137.75	$137.75	$137.70
7 purchase totals =	$703.43		$759.2362	$759.23	$759.25	$759.30