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	$250.46	13.481%	$284.2245	$284.22	$284.20	$284.20
Purchase #2	$189.33	3.480%	$195.9187	$195.92	$195.90	$195.90
Purchase #3	$174.44	12.831%	$196.8224	$196.82	$196.80	$196.80
Purchase #4	$28.69	9.136%	$31.3111	$31.31	$31.30	$31.30
Purchase #5	$59.88	5.298%	$63.0524	$63.05	$63.05	$63.10
Purchase #6	$102.45	7.654%	$110.2915	$110.29	$110.30	$110.30
Purchase #7	$199.58	11.278%	$222.0886	$222.09	$222.10	$222.10
7 purchase totals =	$1,004.83		$1,103.7092	$1,103.70	$1,103.65	$1,103.70