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	$6.94	6.290%	$7.3765	$7.38	$7.40	$7.40
Purchase #2	$104.67	8.419%	$113.4822	$113.48	$113.50	$113.50
Purchase #3	$70.57	9.492%	$77.2685	$77.27	$77.25	$77.30
Purchase #4	$59.34	12.107%	$66.5243	$66.52	$66.50	$66.50
Purchase #5	$97.28	8.168%	$105.2258	$105.23	$105.25	$105.20
Purchase #6	$220.93	13.353%	$250.4308	$250.43	$250.45	$250.40
Purchase #7	$207.37	6.147%	$220.117	$220.12	$220.10	$220.10
7 purchase totals =	$767.10		$840.4251	$840.43	$840.45	$840.40