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	$101.98	6.737%	$108.8504	$108.85	$108.85	$108.90
Purchase #2	$204.73	5.460%	$215.9083	$215.91	$215.90	$215.90
Purchase #3	$58.96	11.157%	$65.5382	$65.54	$65.55	$65.50
Purchase #4	$42.32	7.836%	$45.6362	$45.64	$45.65	$45.60
Purchase #5	$233.93	13.468%	$265.4357	$265.44	$265.45	$265.40
Purchase #6	$103.64	12.460%	$116.5535	$116.55	$116.55	$116.60
Purchase #7	$145.89	6.141%	$154.8491	$154.85	$154.85	$154.80
7 purchase totals =	$891.45		$972.7714	$972.78	$972.80	$972.70