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	$61.48	6.175%	$65.2764	$65.28	$65.30	$65.30
Purchase #2	$112.71	9.658%	$123.5955	$123.60	$123.60	$123.60
Purchase #3	$211.26	5.505%	$222.8899	$222.89	$222.90	$222.90
Purchase #4	$128.61	5.390%	$135.5421	$135.54	$135.55	$135.50
Purchase #5	$38.79	10.185%	$42.7408	$42.74	$42.75	$42.70
Purchase #6	$203.85	8.539%	$221.2568	$221.26	$221.25	$221.30
Purchase #7	$114.57	3.124%	$118.1492	$118.15	$118.15	$118.10
7 purchase totals =	$871.27		$929.4507	$929.46	$929.50	$929.40