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	$112.72	13.515%	$127.9541	$127.95	$127.95	$128.00
Purchase #2	$59.86	9.125%	$65.3222	$65.32	$65.30	$65.30
Purchase #3	$160.27	12.658%	$180.557	$180.56	$180.55	$180.60
Purchase #4	$9.31	9.428%	$10.1877	$10.19	$10.20	$10.20
Purchase #5	$122.62	7.555%	$131.8839	$131.88	$131.90	$131.90
Purchase #6	$56.59	9.568%	$62.0045	$62.00	$62.00	$62.00
Purchase #7	$207.48	7.309%	$222.6447	$222.64	$222.65	$222.60
7 purchase totals =	$728.85		$800.5541	$800.54	$800.55	$800.60