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	$225.43	6.145%	$239.2827	$239.28	$239.30	$239.30
Purchase #2	$220.27	7.665%	$237.1537	$237.15	$237.15	$237.20
Purchase #3	$90.55	13.503%	$102.777	$102.78	$102.80	$102.80
Purchase #4	$217.98	7.314%	$233.9231	$233.92	$233.90	$233.90
Purchase #5	$40.59	12.207%	$45.5448	$45.54	$45.55	$45.50
Purchase #6	$90.43	9.228%	$98.7749	$98.77	$98.75	$98.80
Purchase #7	$210.73	5.355%	$222.0146	$222.01	$222.00	$222.00
7 purchase totals =	$1,095.98		$1,179.4708	$1,179.45	$1,179.45	$1,179.50