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	$177.54	12.263%	$199.3117	$199.31	$199.30	$199.30
Purchase #2	$180.52	7.833%	$194.6601	$194.66	$194.65	$194.70
Purchase #3	$140.27	11.514%	$156.4207	$156.42	$156.40	$156.40
Purchase #4	$219.96	13.167%	$248.9221	$248.92	$248.90	$248.90
Purchase #5	$91.78	3.215%	$94.7307	$94.73	$94.75	$94.70
Purchase #6	$90.61	12.109%	$101.582	$101.58	$101.60	$101.60
Purchase #7	$179.94	3.152%	$185.6117	$185.61	$185.60	$185.60
7 purchase totals =	$1,080.62		$1,181.2390	$1,181.23	$1,181.20	$1,181.20