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	$183.89	7.848%	$198.3217	$198.32	$198.30	$198.30
Purchase #2	$45.43	3.782%	$47.1482	$47.15	$47.15	$47.10
Purchase #3	$198.47	8.483%	$215.3062	$215.31	$215.30	$215.30
Purchase #4	$57.65	3.809%	$59.8459	$59.85	$59.85	$59.80
Purchase #5	$45.74	4.774%	$47.9236	$47.92	$47.90	$47.90
Purchase #6	$172.39	7.584%	$185.4641	$185.46	$185.45	$185.50
Purchase #7	$19.82	3.540%	$20.5216	$20.52	$20.50	$20.50
7 purchase totals =	$723.39		$774.5313	$774.53	$774.45	$774.40