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	$135.69	6.814%	$144.9359	$144.94	$144.95	$144.90
Purchase #2	$92.81	5.695%	$98.0955	$98.10	$98.10	$98.10
Purchase #3	$79.25	11.781%	$88.5864	$88.59	$88.60	$88.60
Purchase #4	$75.79	8.421%	$82.1723	$82.17	$82.15	$82.20
Purchase #5	$87.59	13.668%	$99.5618	$99.56	$99.55	$99.60
Purchase #6	$208.71	12.570%	$234.9448	$234.94	$234.95	$234.90
Purchase #7	$153.67	12.199%	$172.4162	$172.42	$172.40	$172.40
7 purchase totals =	$833.51		$920.7129	$920.72	$920.70	$920.70