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	$250.60	9.830%	$275.234	$275.23	$275.25	$275.20
Purchase #2	$213.64	4.333%	$222.897	$222.90	$222.90	$222.90
Purchase #3	$28.57	9.758%	$31.3579	$31.36	$31.35	$31.40
Purchase #4	$174.46	7.432%	$187.4259	$187.43	$187.45	$187.40
Purchase #5	$201.40	12.500%	$226.575	$226.58	$226.60	$226.60
Purchase #6	$28.46	10.719%	$31.5106	$31.51	$31.50	$31.50
Purchase #7	$97.34	9.829%	$106.9075	$106.91	$106.90	$106.90
7 purchase totals =	$994.47		$1,081.9079	$1,081.92	$1,081.95	$1,081.90