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	$30.48	7.867%	$32.8779	$32.88	$32.90	$32.90
Purchase #2	$149.27	5.773%	$157.8874	$157.89	$157.90	$157.90
Purchase #3	$114.90	13.266%	$130.1426	$130.14	$130.15	$130.10
Purchase #4	$50.32	10.743%	$55.7259	$55.73	$55.75	$55.70
Purchase #5	$205.55	4.802%	$215.4205	$215.42	$215.40	$215.40
Purchase #6	$85.80	5.424%	$90.4538	$90.45	$90.45	$90.50
Purchase #7	$103.80	5.139%	$109.1343	$109.13	$109.15	$109.10
7 purchase totals =	$740.12		$791.6424	$791.64	$791.70	$791.60