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	$54.35	9.127%	$59.3105	$59.31	$59.30	$59.30
Purchase #2	$69.25	8.463%	$75.1106	$75.11	$75.10	$75.10
Purchase #3	$176.59	8.395%	$191.4147	$191.41	$191.40	$191.40
Purchase #4	$64.61	5.353%	$68.0686	$68.07	$68.05	$68.10
Purchase #5	$56.66	12.484%	$63.7334	$63.73	$63.75	$63.70
Purchase #6	$94.32	5.435%	$99.4463	$99.45	$99.45	$99.40
Purchase #7	$81.73	11.202%	$90.8854	$90.89	$90.90	$90.90
7 purchase totals =	$597.51		$647.9695	$647.97	$647.95	$647.90