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	$133.99	4.136%	$139.5318	$139.53	$139.55	$139.50
Purchase #2	$83.53	6.670%	$89.1015	$89.10	$89.10	$89.10
Purchase #3	$84.41	7.148%	$90.4436	$90.44	$90.45	$90.40
Purchase #4	$63.73	7.632%	$68.5939	$68.59	$68.60	$68.60
Purchase #5	$79.77	6.627%	$85.0564	$85.06	$85.05	$85.10
Purchase #6	$242.93	5.405%	$256.0604	$256.06	$256.05	$256.10
Purchase #7	$39.26	3.369%	$40.5827	$40.58	$40.60	$40.60
7 purchase totals =	$727.62		$769.3703	$769.36	$769.40	$769.40