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	$95.30	5.165%	$100.2222	$100.22	$100.20	$100.20
Purchase #2	$250.84	8.222%	$271.4641	$271.46	$271.45	$271.50
Purchase #3	$179.91	12.558%	$202.5031	$202.50	$202.50	$202.50
Purchase #4	$85.99	7.574%	$92.5029	$92.50	$92.50	$92.50
Purchase #5	$178.78	3.234%	$184.5617	$184.56	$184.55	$184.60
Purchase #6	$67.92	6.348%	$72.2316	$72.23	$72.25	$72.20
Purchase #7	$200.32	9.728%	$219.8071	$219.81	$219.80	$219.80
7 purchase totals =	$1,059.06		$1,143.2927	$1,143.28	$1,143.25	$1,143.30