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	$135.50	5.619%	$143.1137	$143.11	$143.10	$143.10
Purchase #2	$159.53	5.771%	$168.7365	$168.74	$168.75	$168.70
Purchase #3	$128.76	10.713%	$142.5541	$142.55	$142.55	$142.60
Purchase #4	$29.96	10.345%	$33.0594	$33.06	$33.05	$33.10
Purchase #5	$26.85	6.706%	$28.6506	$28.65	$28.65	$28.70
Purchase #6	$117.48	8.186%	$127.0969	$127.10	$127.10	$127.10
Purchase #7	$166.69	8.807%	$181.3704	$181.37	$181.35	$181.40
7 purchase totals =	$764.77		$824.5816	$824.58	$824.55	$824.70