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	$89.89	11.646%	$100.3586	$100.36	$100.35	$100.40
Purchase #2	$64.79	6.751%	$69.164	$69.16	$69.15	$69.20
Purchase #3	$197.53	4.610%	$206.6361	$206.64	$206.65	$206.60
Purchase #4	$102.56	10.713%	$113.5473	$113.55	$113.55	$113.50
Purchase #5	$71.57	9.732%	$78.5352	$78.54	$78.55	$78.50
Purchase #6	$27.32	12.708%	$30.7918	$30.79	$30.80	$30.80
Purchase #7	$115.63	12.803%	$130.4341	$130.43	$130.45	$130.40
7 purchase totals =	$669.29		$729.4671	$729.47	$729.50	$729.40