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	$44.74	11.511%	$49.89	$49.89	$49.90	$49.90
Purchase #2	$85.88	9.242%	$93.817	$93.82	$93.80	$93.80
Purchase #3	$228.94	7.321%	$245.7007	$245.70	$245.70	$245.70
Purchase #4	$247.69	13.168%	$280.3058	$280.31	$280.30	$280.30
Purchase #5	$74.41	9.248%	$81.2914	$81.29	$81.30	$81.30
Purchase #6	$34.42	5.386%	$36.2739	$36.27	$36.25	$36.30
Purchase #7	$100.72	12.113%	$112.9202	$112.92	$112.90	$112.90
7 purchase totals =	$816.80		$900.1990	$900.20	$900.15	$900.20