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	$188.69	6.373%	$200.7152	$200.72	$200.70	$200.70
Purchase #2	$178.70	3.141%	$184.313	$184.31	$184.30	$184.30
Purchase #3	$239.43	6.850%	$255.831	$255.83	$255.85	$255.80
Purchase #4	$220.63	8.300%	$238.9423	$238.94	$238.95	$238.90
Purchase #5	$30.32	3.645%	$31.4252	$31.43	$31.45	$31.40
Purchase #6	$155.44	12.467%	$174.8187	$174.82	$174.80	$174.80
Purchase #7	$114.88	13.712%	$130.6323	$130.63	$130.65	$130.60
7 purchase totals =	$1,128.09		$1,216.6777	$1,216.68	$1,216.70	$1,216.50