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	$166.91	4.801%	$174.9233	$174.92	$174.90	$174.90
Purchase #2	$245.66	10.115%	$270.5085	$270.51	$270.50	$270.50
Purchase #3	$103.43	6.854%	$110.5191	$110.52	$110.50	$110.50
Purchase #4	$47.39	9.612%	$51.9451	$51.95	$51.95	$51.90
Purchase #5	$29.65	7.511%	$31.877	$31.88	$31.90	$31.90
Purchase #6	$236.72	11.153%	$263.1214	$263.12	$263.10	$263.10
Purchase #7	$186.64	5.758%	$197.3867	$197.39	$197.40	$197.40
7 purchase totals =	$1,016.40		$1,100.2811	$1,100.29	$1,100.25	$1,100.20