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	$238.73	7.658%	$257.0119	$257.01	$257.00	$257.00
Purchase #2	$174.79	5.686%	$184.7286	$184.73	$184.75	$184.70
Purchase #3	$83.51	10.705%	$92.4497	$92.45	$92.45	$92.40
Purchase #4	$173.90	6.623%	$185.4174	$185.42	$185.40	$185.40
Purchase #5	$67.97	3.729%	$70.5046	$70.50	$70.50	$70.50
Purchase #6	$250.70	9.843%	$275.3764	$275.38	$275.40	$275.40
Purchase #7	$100.72	9.578%	$110.367	$110.37	$110.35	$110.40
7 purchase totals =	$1,090.32		$1,175.8556	$1,175.86	$1,175.85	$1,175.80