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	$99.47	7.337%	$106.7681	$106.77	$106.75	$106.80
Purchase #2	$25.89	3.355%	$26.7586	$26.76	$26.75	$26.80
Purchase #3	$50.97	5.767%	$53.9094	$53.91	$53.90	$53.90
Purchase #4	$104.74	3.277%	$108.1723	$108.17	$108.15	$108.20
Purchase #5	$99.89	9.250%	$109.1298	$109.13	$109.15	$109.10
Purchase #6	$143.91	10.677%	$159.2753	$159.28	$159.30	$159.30
Purchase #7	$92.91	10.381%	$102.555	$102.56	$102.55	$102.60
7 purchase totals =	$617.78		$666.5685	$666.58	$666.55	$666.70