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	$245.69	4.229%	$256.0802	$256.08	$256.10	$256.10
Purchase #2	$213.74	5.742%	$226.013	$226.01	$226.00	$226.00
Purchase #3	$114.45	7.468%	$122.9971	$123.00	$123.00	$123.00
Purchase #4	$120.98	7.774%	$130.385	$130.39	$130.40	$130.40
Purchase #5	$71.45	5.364%	$75.2826	$75.28	$75.30	$75.30
Purchase #6	$125.64	9.761%	$137.9037	$137.90	$137.90	$137.90
Purchase #7	$52.82	3.381%	$54.6058	$54.61	$54.60	$54.60
7 purchase totals =	$944.77		$1,003.2674	$1,003.27	$1,003.30	$1,003.30