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	$209.87	6.493%	$223.4969	$223.50	$223.50	$223.50
Purchase #2	$168.92	6.830%	$180.4572	$180.46	$180.45	$180.50
Purchase #3	$136.66	12.855%	$154.2276	$154.23	$154.25	$154.20
Purchase #4	$42.90	7.498%	$46.1166	$46.12	$46.10	$46.10
Purchase #5	$31.34	6.152%	$33.268	$33.27	$33.25	$33.30
Purchase #6	$202.27	8.513%	$219.4892	$219.49	$219.50	$219.50
Purchase #7	$23.59	6.591%	$25.1448	$25.14	$25.15	$25.10
7 purchase totals =	$815.55		$882.2003	$882.21	$882.20	$882.20